I don't think that IIIPro believes they have any problems or issues with the E4s. I complained to them once and they weren't very helpful at the time.
I am beginning to believe that there is some problem with the E4 levers that somehow develops a void or air somewhere in the lever hydraulics. Could be caused by "improper" bleeding, or lack of technique by me. Who knows. I haven't seen many complaints about the E4s other than me.
I am also beginning to form an opinion that for some reason on my bikes with rear brake internal hose routing, I am unable to get all of the air bubbles out of the system and this come back to haunt me later. Seems like when I bleed the brake off the bike such that I can freely move the lever assembly and calipers in all sorts of directions, I am able to get all the bubbles out.
The new R2X4 and R3X4 have different levers and seemingly the same calipers. I can't seem to find information on whether I can use BH90 brake hose, compression nuts, olives for them. They are advertising a reusable no olive system, but I am sure that will leak, I don't trust it.
Have you tried bleeding with the lever at a 45 degree angle? I know some brakes have to be angled rather than level, I can see how at certain angles air wouldn't be able to escape. But I don't understand how that air could suddenly pop up in the system, must be a really poorly designed master cylinder.