In round 3 Gane was holding onto a Kimura for 2+ minutes with no chance of finishing it. When you attack a kimura from the bottom without actually sweeping your opponent with it, you aren't doing any damage and you sure as shit aren't even close to finishing the fight if you never get it even close to extended.
What you are doing essentially becomes stalling - you end up just holding onto a set-up that will never turn into a realistic submission attempt and gassing yourself out in the process. By going for that kimura Gane conceded to being stuck on the bottom for the entirety of the round and didn't do anything to scramble, throw shots, force transitions, because he was so tired from holding the kimura grip and trying to force a sub that wasn't there.
Every judge gave Volkov round 3 and 97% of fan votes on MMA Decisions gave Volkov round 3 - the fact that someone as knowledgeable as you thinks it's "up for debate" I find rather shocking. There is a case to be made for Gane winning round 2, though I don't see it, but there is no way in hell he did enough of anything to deserve round 3. I even think round 1 was pretty close, just Gane getting an actual deep submission attempt (even if was never going to finish it) at the end of the round swings it in his favor.