I’m using OnlyOffice docs and I was writing out a concept for a story idea I’ve been working on. Everything looked normal, but suddenly the Spell Check underlined every instance of the word “that” and “is” in my document. Of course every instance was spelled correctly. I saved my file and re-opened my document and the issue had gone away, however, now the word “alley” is underlined and if I right click for suggestions, it wants to replace it with “alley” and if I do, it remains underlined. Very bizzare, so I thought I would mention it here. I’ve attached a screenshot with most of the copy redacted, but it shows that everything underlined is actually spelled correctly. To fix the alley issue, I had to add it to my Dictionary, even though it was already a suggestion in the dictionary, and as I said it was already spelled correctly.
This sort of incorrect spelling error tagging has been happening in every document I create, seemingly sporadically.
Hi @TorQueMoD
In you enthusiasm to post an issue, you forgot some potentially relevant details of OnlyOffice version number, and the platform that you are running OnlyOffice on; Win/Mac/Linux, and its version.
I’m quite certain someone from OO Support will ask for those.
You should also supply the details of Text Language and the Document Language. That is this setting;
in the bottom status bar.
Obviously words like; “that”, “is, and “alley” are normal English words, for both the King’s English and that US English, so don’t be surprised if a suggestion of re-installation is made, in case a language file got corrupted somehow.
I’ve noticed it across multiple versions which is why I didn’t bother posting my version, but it’s 8.3.3.21
Language is English United States.
The current version is 9.4.
You could try uninstalling OO, And then reinstalling the current version.
If the issue persists, you can update this thread, and also advise what platform you are running, as this could be relevant.
oh, wow. I guess there’s no built in auto updater then. Downloading the latest version now.
Thank you 
Actually there is a built-in update, at least on Windows where I have seen, and use it.
I just suggested the uninstall and install to ensure any libraries and data files were updated.
If your issue is related to a corrupted language file, this may correct it. Maybe.