After 3+ years you'd think they might have given up on fixing it
You are assuming that they tried, or are trying, to fix it, and then gave up.
Consider the possibility that they have not tried to fix it.
I seem to recall the "official" line was that they could not fix it because it was difficult to duplicate. I would imagine it would not be difficult to duplicate at all. Just have 2 people continue to play coin matches against each other, each time someone forfeits, other times, they simply close their game app without exiting game. You would think, at some point, it would be duplicated.
As long as people play coin rooms, and showdowns, without any fix, there really is no priority to fix it - IMO.
A glitch that results in loss of revenue would certainly have top priority; this is not one of them.