With iOS 14, Apple added an additional setting to the Privacy settings for Photos. In some cases, this can cause the Multi-Add option within Site Audit Pro to be unable to add photos.
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.)