The fix for this issue is now available in the latest update of InDesign – that is, InDesign 15.0.3.
Please update your InDesign application to get the fix.
Adobe InDesign team
An error occurred while saving the commentAnonymous commented
I am using ID v.15.1.2 and this is still happening – Spellchecker doesn't recognise even the simplest words and then after a short while, just crashes the programme. Not at all helpful in a professional tool such as this is supposed to be!