In my tests, the restart occurs about 8-10 seconds after closure. In the forum, @bruceqld called it an unCrash, so I adopted the term:
-a V4.?? file opened in V5.2 will not cause the unCrash.
-a v4.?? file opened in V5.2, then saved in V5.2 will not unCrash either.
-a v5.0 < V5.2 file opened, whether resaved or not WILL cause the unCrash.
..based on my testing of the files I had on hand. So it may be a V5.2 issue that affects V5 files prior to V5.2.
My Windows was at the version from April of last year (2004), so I upgraded it to the latest 20H2 version. It didn't change a thing with this Studio One issue. A stab in the dark would be that is somehow related to the new "safe" restart capability in V5.2, but again that's just a guess.
EDIT: at least one forum member confirmed that the unCrash can occur in originally created v5.2 files.