I was surprised to get no real matches when I searched the LR Classic board for "check spelling while typing". Surely someone else has asked that this setting (Edit-Spelling-Check Spelling While Typing) remember its last value (on MacOS, it doesn't. I know about Windows). As it is, I have to re-enable it each time I restart LR, usually in the middle of captioning when I have to go back and check that previous captions were correctlty spelled.
Adobe, this must be the easiest of changes to make. Next release, please? 🙂