Which platinum game? Which known problem? I wish complaints were less vague, then it wouldn't sound like exaggeration and would be actionable for people who are working on these technologies.
For what it's worth, I've played dozens of platinum (and gold, and silver) games since Proton came out with nearly flawless experiences. In many cases, it ran more reliably than Windows.
Valfaris is rated platinum on protondb, and it crashes on launch for me, same with Titan Quest, which is rated gold. Proton has been a godsend for gaming on Linux, but I don't put much stock in protondb beyond checking to see if a game is known to not run at all.
I hope you reported your experience as well then? This is a user-maintained database, so unless people keep putting in their information, it will not be accurate/complete.
For what it's worth, I've played dozens of platinum (and gold, and silver) games since Proton came out with nearly flawless experiences. In many cases, it ran more reliably than Windows.