Spellcheck slowdown

In my writer document (now at 284k words), spellcheck slowed down a lot. It underlined a word, I added that the the dictionary but the underline didn’t go away for about 10 sec.
After restarting the document it worked fine.
I’m just curious if that happened because I pasted about 50k words into it and then over those or was it something else?

Why do you hope to get an answer with your meager information?
Nobody has binoculars to look at your screen or system.
You don’t give any information about:

  • Which operating system do you use?
  • Which LibreOffice version?
  • In which file format do you save?

    You can also upload your file here so that someone can examine it.
    To upload, edit your initial question and use the upload icon.

When you paste in some 50 K words, Writer will format the insertion, stuff like pagination and of course run the spell checker over it. That will, of course, take some time, even on the fast computers of nowadays. MS Word, when I still used it, and that’s years ago, would at some point while I was editing a document, warn me that there were so many spelling errors (i.e. unrecognized words), that it stopped tracking them.

I remember Word doing that too. Also, my computer isn’t that fast. It’s a mid range from 2014.
I figured that it was the pasting and it processing that took a while.