I do not know if it is a bug or a feature: For testing purposes of CLDR in context of Wikidata I have created https://test.wikidata.org/wiki/Q149653 some months ago.
Since a few days statements for monolingual text shows " The value's type "monolingualtext" does not match property's type "string". "
Adding @Jakob_WMDE as this week's incident manager to check if this is just a weird glitch or something more serious.
This likely has to do with some faulty config changes that were done recently. I believe this is a symptom of T208488 and is still broken due to resource loader caching. Purging the page "solved" the problem.