See https://3v4l.org/8ENBl trigggers a warning in the logs:
PHP Warning: preg_match(): Compilation failed: nothing to repeat at offset 15 in plugins/CustomDimensions/Dimension/Extraction.php on line 117
Ideally, in all plugins where it is possible to define a regex, we validate that the regex is at "valid". For example Goals etc. This will increase the correctness of the tracked data.