CI variable cannot be set - Validation failed

Description of the problem

I cannot set a variable with a name, that should fit the rules for subgroups, it works fine

Which Group/Project (with full path) is experiencing the issue?

alpiq_cicd

Approximate date/time when the error occurred.

31.3.2020 15:10

Describe what you were doing right before the issue occurred.

I opened the variables section and attempted to set a variable.