Probably to fix this security vulnerability, Apple tightened up security again with the publishing of macOS 11.4 in month May of year 2021.  It is possible that this may have also been rolled into a security update to macOS 10.15.7 which they pushed out on 2021 September 13.  Although we duly tested their beta and notified Apple in the appropriate forum of the possible unintended consequences, Apple did not respond and proceeded to publish 11.4 without providing any guidance to users or developers.

It seems that there are two changes in macOS 11.4 which broke stuff for our users:

1.  It may have switched off Full Disk Access for our app (Apple FB9103124).
2.  More importantly, it added a new requirement that you also enable Full Disk Access for our app's Agent as well as the app itself (Apple FB9120467).

To fix it, please perform our newly updated procedure for granting Full Disk Access.

We are working on a more convenient fix for future versions of our apps.