Thanks for reopening this and for the screenshots. I found the cause.
This is the same intermittent macOS rendering problem, but it was occurring through a different autocomplete popup. The previous fixes covered Studio’s main type fields and code-editor completion windows. The method Parameters field has its own specialised popup, and that one had been missed.
When its list of suggestions narrowed, the native macOS popup resized and could stretch its contents. This is why the problem did not happen every time and could not be reproduced on every Mac.
I’ve moved this remaining popup into Studio’s internal overlay layer, added a regression test for it, and audited the other autocomplete popup paths. The fix will be included in the next release: https://feedback.objo.dev/bug/1443
