This same bug appears in Selectrum, I'm fairly certain this is something to do with window properties or the like rather than minibuffer.el etc.
This is apparently actually a long standing bug in truncate-lines, combined with window-resize; it was later fixed ... in GNU Emacs 28. Commenting out the truncate-linets from the initialization for this minor-mode makes it usable, as does setting resize-mini-windows to nil. I've done the latter, but this isn't a permanent fix and I'll still need to revisit in the future.