Sandboxie-Plus 1.17.3 was released less than 24 hours ago, maybe this also resolves this issue for you.
I had seen that issue on Windows 7, with several previous versions of Sandboxie-Plus in combination with a video player, but could not reproduce it reliably. Recently I upgraded to Windows 11, where I did not encounter the issue with.
If it still happens, on which platform do you use Sandboxie-Plus? (e.g. Windows 7, Windows 10, Windows 11, Windows 10 ARM, Windows 11 ARM) (24H2, 25H2, build number, like 26200.8037) Does it occur with specific software?