LO Writer 6.4 starts an stop spell checking

I am running LO on macOS 10.15 on my mid 2012 i7 16GB MacBook Pro. My language is en_US. Spell checking works on some document and not on others. On some documents it starts and stops. I have Tools | Languages | For All Text set to English. The styles all have English (USA) set. My LO | Preferences | Language Settings are all set to English (USA)

Since I am a poor typist, I really need the spell checker. Any suggestions on troubleshooting this?

  1. Read this tutorial.
  2. If you can’t find an answer, refine your question.

In particular,

works on some document and not on others

Are all those documents produced by you or obtained from other sources? Share a sample document where the spellcheck fails.