I found two (2!) bug reports about this happening, no bluepost/answer/confirmation, no proof. I'm 99% confident to say your claim is wrong, not sure where you got that from.Įdit: Did some research. And if 0% upgrades were possible we'd see 100+ ranks on Asia already. I have never failed a 100%, i have never heard of anyone of my friends, clan mates, or streamers fail a 100%. That's a sample size of about 2500 on 100% upgrades. I have upgraded close to 50 gems to rank 50 or higher on non-season in S1/S2/S3 (I need a goal in GRs, so upgrading the 7th backup Bane of the Trapped helps me get through it). This is why few players failed to upgrade gem at 100%.
The problem is that those values are never 0 and 100 but very close to them.
There is a chance to upgrade 0% and to fail at 100%.