That was a very long message to say: have you tried unplugging it and plugging it again?
You could work in IT support now, you know enough to fix 90pc of people's problems!

My main hypothesis is that I didn't plug the cables properly into the battery, and that the vibrations from being transported in a care shook them loose. Then when I started riding, the movement caused just enough of a connection to be established so I could shift.

Assuming that's the cause, does anyone have suggestions for how to better secure the cables at the battery end?

Another hypothesis is that the issue was caused by dodgy batteries in the battery holder. I don't have anything to support this hypothesis currently, apart from the fact that I'm using unbranded batteries from eBay (https://www.ebay.com.au/itm/256250808223). They've been charging fine, and the reported charge hasn't dropped much with each ride. Regardless, I now have a branded set on order.

I'd suggest either heat shrink plastic, hot glue or rubber cement. I actually didn't use any adhesive at the battery holder end for my ER9 build. I just made sure the cables were properly snug. I'm using bubble wrap packaging tied to a string to secure the battery holder inside my seat post. I just used the bubble wrap that came with the groupset. I'm wondering if this stuff makes for a better vibration insulator than using those fancy Di2 mounts? My cables on the FD/RD end are all rubber cemented in and I added coat of dielectric grease.

Anyways, I've transported my bike multiple times on a car bike rack and I regularly ride on rough surface roads. Also I'm using Ebay batteries as well with no problems.

I’ve bult wheels with CX Rays, Wing 20s/Pillar 1420s and CN494 spokes. I couldn’t really tell much of a difference with any of them neither when building nor when riding. Maybe I’m not the most sensitive person in that regard. The quality of the threads was maybe slightly less refined on the CN spokes. They cost half as much as CX Rays so that’s to be expected, I guess. The Pillars have a slightly longer round section before they’re bladed IIRC. But no big difference at all. These days I’d probably build with whatever’s readily available in the desired length.

eR9 issue and fix

I had an issue with my L-TWOO eR9 groupset today that I later fixed. It was most likely user error, and I'm posting it here in case it could help someone else in the same situation.

tl;dr
Problem: The front derailleur wouldn't shift, but the rear derailleur shifted just fine.
Fix: Ensure both derailleurs are firmly plugged into the battery, by unplugging them at the battery end, and firmly plugging them back in.
Likely reason: Poor connection to the seatpost battery on the battery end, possibly caused by vibrations by being transported in a car.
Other plausible reason: Dodgy batteries.

Situation

I was going for a ride in the morning, and I loaded my bike (https://chinertown.com/index.php/topic,4952.0.html) in the boot (trunk for those of you in the US) of my sedan (saloon for those of you in the UK), lying on the side (NDS). The drive to the start of the ride took about 20 minutes. When I took my bike out of the car, the rear derailleur shifted just fine, but the front derailleur wouldn't budge.

I tried the following:

• Shift using the shifters
• Shift using the app
• Unplug the rear derailleur, wait 10 seconds, then plug it back in
• Unplug the front derailleur, wait 10 seconds, then plug it back in
• Calibrate the front derailleur using the app
• Adjust front gears using the app
• Change front derailleur high and low limits in the app
• Swap the gear shift responsibilities of the left and right shifters
• Try with one-touch shifting both on and off
• Try with gear protection both on and off
• Rear derailleur firmware update - was using version 0.1.1, no updates available
• Front derailleur firmware update - app reported current version 0.0 and latest 0.0
• Reset to factory settings - this reset all my derailleur position settings (which I fortunately had saved)

The only response I got from the front derailleur was when I plugged the front derailleur cable back in. It was a buzz reminiscent of Trace Velo's issue (https://youtu.be/32UDzOrqK2I?t=78s).

Other behaviour I noticed:

• The app reported 91% battery level.
• The app reported that I used the latest rear derailleur firmware version 0.1.1
• The app reported that I used the latest front derailleur firmware version 0.0. This was different to what it previously reported, which was 1.12
• The app would show that the front gears had changed when I used the app, but nothing happened.
• When I tried to adjust the front derailleur position for the large chainring in the app, the app showed a position of 0. This doesn't match what I saw from Trace Velo's video. The position for the small chainring showed correctly what I had set it to previously (12).

Other points of note:

• The app reports that I'm using model ES-R9001.
• The serial number on the rear derailleur starts with 250123.
• The battery holder uses coil springs rather than leaf springs to hold the batteries in place.
• I'm running the groupset as 2x11.
• I haven't ridden the bike in the rain or on wet roads, and I haven't washed the bike.

At this point I thought the rear derailleur was toast (which apparently was Trace Velo's problem in the end), but I decided to do a short solo ride anyway, with the front stuck in the small chainring. After riding for about 50 meters, I tried to change to the large chainring, and it shifted! Actually, it over-shifted, because I had lost my position settings when I "Reset to factory settings". So I stopped, put the chain back on, and tried to shift down. No response. The rear still shifted just fine. I then proceeded to try many of the steps listed above one more time, but no luck.

So I started riding again, and after another 50 meters of so, I could shift back to the small chainring. That was the last time the front derailleur shifted until I got back home, so put my rear derailleur position adjustments back as they were and did the ride in the small chainring. It was fairly hilly, so I could at least get up the hills!

After I got back home, the front still wouldn't shift. At that point, I wanted to check the connections on the battery end. So I pulled out the seatpost carefully, as I wanted to see what state the connections were. But as I pulled the seatpost slowly and carefully up and out, both derailleur cables came loose from the battery case connectors. I then plugged both of the cables into the battery holder, and immediate success! I could shift up or down without issue as before, and the front derailleur firmware now showed the correct version.

My main hypothesis is that I didn't plug the cables properly into the battery, and that the vibrations from being transported in a care shook them loose. Then when I started riding, the movement caused just enough of a connection to be established so I could shift.

Assuming that's the cause, does anyone have suggestions for how to better secure the cables at the battery end?

Another hypothesis is that the issue was caused by dodgy batteries in the battery holder. I don't have anything to support this hypothesis currently, apart from the fact that I'm using unbranded batteries from eBay (https://www.ebay.com.au/itm/256250808223). They've been charging fine, and the reported charge hasn't dropped much with each ride. Regardless, I now have a branded set on order.

I'll also keep this bike for shorter trips for the time being, and be ready to pull out the seatpost should the problem reappear.

. Looks great!   Sad to say they definitely don't clear coat but rather buff the color to a gloss finish instead.  Only if you order a chameleon color it seems that it's clear coated due to the process of painting Chameleon colors

Yes, you are probably right.
After knowing that, I would definitely choose a chameleon color, if ordering again.
So maybe a good tip for others who are interested in this frame.