With iOS 14, Apple made changes Privacy settings on iOS. In some cases, during later iOS updates, these settings seem to sometimes "reset", causing the Multi-Add option within Site Audit Pro to not work correctly.
To fix this, please do the following:
1) Access your device's Settings.
2) Tap on "Privacy".
3) Tap on "Photos"
4) Tap on "Site Audit Pro".
5) Tap on "All Photos". (If "All Photos" is already selected, select "None", then go back to the previous screen. From there, tap "Site Audit Pro" again to and then tap on "All Photos" - this will refresh the setting.)