Grammarly is all in on AI and recently started recommended splitting "wasn't" and added the contraction to the word it modified. Example: "truly wasn't" becomes "was trulyn't"
Even in British I'm not sure how widely they actually use it - do they say "I've a car" and "I haven't a car"?
Contractions are common in Australian English to, though becoming less so due to the influence of US English.
Has to be a bug in their rule-based system?