Apple Mail resets custom width of preview/inbox list pane

Mail client resets custom width of mail preview/inbox list slider pane. Cannot find out what triggers it. Seems to happen after I leave the computer for a while. However, I just tried putting to sleep, closing window, quitting and relaunching, and switching windows. For now it is remembering the size I set it to. But eventually I'll go back and it will be changed back to whatever default it keeps going to.

Tahoe 26.1

M4 macbook pro