The bug occures when the scoreboard's or tag's name contains special characters, like "é" or "#". It is also impossible to remove, modify or setdisplay scoreboards that exist with commands.
MC-134750
Special characters in scoreboard/tag name does not work
Resolved
Works As Intended
0
These characters were indeed previously allowed, but didn't function properly (any detection with them failed, see MC-55348; this change is to prevent that from ever occurring).