LO should spell check last word in document even if there's no white space after it. Last 'tezt' in one and only sentence in document - should get underlined.
Maybe can even be implemented that LO underlines misspelled word if word inactive for more then four seconds (that is if somebody stopped typing).
Three seconds it not enough for those who can't type fast, in five I already save and exit so I could still misspell that last word.
Also, when opening/loading existing file from hard drive, LO should preform spell check of entire document throughout the document without time delay.
On open, it should do what it supposed to do.
But while editing, four seconds delay is fine because it would be awful that it's underlining word you're actually typing.
Maybe there are ways to figure out are you typing or not, instead of that four (or what ever) seconds delay.
Still present in LO 126.96.36.199 on Debian Buster (curr testing).