I was recently trouble shooting an issue I've been having with my sandbox not auto-deleting when I download files from my browser and invoke the immediate recover feature in this thread. I was told I technically don't have the latest release. Upon checking, the one recommend was v1.14.3 / 5.69.3. However I see this is listed in the "Preview" builds section. My current version is v1.13.7 downloaded from the main page and listed as "Stable" (and says I'm up-to-date when I run the updated checker in the app). The latest preview build is from last week, and mine is from back in May. Is the "Preview" build still considered a type of beta, where bugs are still being worked out? Not sure what the differences are between these (since the newest one is marked as a "Release" on GitHub) vs being a "Stable" release available on the main site. Thanks!
I have always installed previews (straight over the top of the previous build) and not really had any problems with them. As a test, perhaps try unticking immediate file recovery (click apply) which will invoke quick recovery which will ask you to recover downloaded files when you close the browser, and then select to delete the contents left. Don't forget to check your delete box options setting. https://sandboxie-plus.com/downloads/