Spell Checker - have to run it several times to find the errors. Running LO

I have a large text document in Writer and then run spell check. Run it once and if finds errors to fix which I correct and save the document. Run it again and it finds more errors - fix and save. Do the same again and after about 4 or 5 runs it finds no new errors. Especially on something like - first word of a sentence not in upper case! Is there some setting to change? Update? So it works but it does not work efficiently. Is there someway to improve it?
Thanks in advance for any help.

User Interface = English (UK) (no Australia option)
Locale setting = English (Australia)
Default language for documents = English (UK)
Hunspell Spell Checker is ticked
User defined dictionaries = English (UK) and English (USA)
Check spelling (and grammar) as you type are ticked
Check upper-case words is ticked!

You should improve your question. In particular:

  1. What is the file format that you save your document to? What is/are the actual language(s) of the document (rather than the default)?
  2. How big is it?
  3. You write: something like - first word of a sentence not in upper case. But it has nothing to do with spelling. It is a grammar issue. So what is your question really about?