by Ken Task.
@Dennis .... Welcome!
Ahhhhh the 'mysteries of Moodle' .... hmmmm ...
https://docs.moodle.org/311/en/Errors_FAQ
One item not present is setting theme to one that comes with version.
Even in https://docs.moodle.org/311/en/Category:Error
setting_invalid_ui_label doesn't appear.
Now the questions are how does a label get entered as 'blank' or go blank and why did Klass not show it?
Like I said ... the 'mysteries of Moodle'!
All is well that ends well! Merry Merry and Happy New Year in 2022 (we all could use one!)!
'SoS', Ken