I made a script for my organization which copies entire GDB files to new locations using UNC paths. The script functions successfully in ArcGIS Pro in the desktop toolbox. I shared the script as a web tool, and the copy function now receive the "Error 000260: Failed to copy" and "Error 999999: Something unexpected caused the tool to fail" with the same parameters.
The line which fails is arcpy.management.Copy(GDB, newGDBpath).