I finally managed to fix the chain line issue on my setup. My BB is 90.5mm (BBRight). As others have pointed out with chainring issues, the same problem exists with the spider. The machining quality is poor - some tabs on the spider are 3.4mm thick, while others are 3.6mm. The spacers included are also the cheapest imaginable, and their thickness is inconsistent (not 1.5mm but 1.4mm or 1.6mm instead). I think the chain line problem comes from the spider’s incorrect depth.
I’m using Ultegra 11-speed, and to resolve the chain line issue, I had to add 3mm spacers to the drive side. However, this left no room for preload adjustment, and tightening the crank bolt added extra stress on the bearings. Additionally, with the 3mm spacers, the crank arms were no longer centered relative to the rear wheel. I figured that if I used 1.5mm spacers on the non-drive side and adjusted the preload ring by ~1.5mm, I could center the crank arms. While this helped, the chain line worsened, as the spider was pushing the chain too far in, causing it to rub against the inner plate of the front derailleur.
Here I realized the spider itself was the issue. After searching online, I found a replacement spider from Stone with similar dimensions but slightly less depth. I decided to take a chance and ordered it, and thankfully, it worked. The new spider had a ~1.5mm shallower depth, reducing the need for 3mm spacers to just 1.5mm, and I could finally use the preload ring. The chainring tabs on the Stone spider were also properly machined, with a uniform thickness of 3.5mm, similar to Shimano’s. I slightly adjusted front derailleur and everything looks okay for now, however I haven’t been able to properly test it outside yet, as it’s winter here.
Initially, I wanted to return the crankset. The seller contacted me, begging not to return it through AliExpress, as he’d lose money and the crankset would just be recycled somewhere at AliExpress's warehouse. He promised to cover all costs if I shipped it directly back to China. I asked him if he can provide any solutions and decided to give him a chance, but after two weeks of vague promises and no real solutions, I found my own fix and asked him to compensate me for the replacement spider. At first, he claimed it was too expensive and suggested splitting the cost 50/50, but eventually, he agreed to cover the full amount. However, it’s been nearly two weeks since then, and I still haven’t received any refund. Now I'm being simply ignored.
So, I DO NOT RECOMMEND buying this crankset unless you’re confident you can handle the issues yourself. The crank arms and spindle look good, the rest is bad, and if anything breaks, don’t expect much in terms of support. While I’ll probably keep the crankset, I’m still unsure about its reliability since I haven't tested it outside.