https://bugs.winehq.org/show_bug.cgi?id=56110
--- Comment #3 from Béla Gyebrószki gyebro69@gmail.com --- (In reply to Zeb Figura from comment #2)
Ugh, found it, sent merge request 4756. It was a race after all. I have no idea how it was so incredibly consistent in that case, or how a single client-side trace would make the difference every time, but there you go.
The patch fixes the problem for me, thank you.