Hey @godfatherjohn, 
Thanks for the detailed information and for confirming it’s tied to the keyboard layout switching back to the previous document’s language. We’re investigating this alongside a related issue reported here: Presentation Editor Spell Checker Language Auto-Revert.
Big thanks for staying active and helping out on community.onlyoffice.com!
We’ll keep digging and update you in this thread as soon as we have progress. 