Form calculation fields not working

Neither of the three calculation fields (Value, Simplified field notation, Custom calculation script) will save anything when I edit them. They just revert to greyed out after I have finished adding a calculation, does not matter what I input, I've tried everything.

This is on a blank document created in Acrobat Pro and saved locally to my hard drive. The weird thing is I have another cloud pdf doc where calculations work just fine.

After some experimentation, I tried copying a working field from the other document to the blank document. Then the Simplified field notation field would save correctly, and I was able to change the formula to fit my field names in the blank document. But if I change this field to a Value and try to pick the fields, we're back to not saving anything. If I then go back to Simplified field notation and input anything, it now won't save, so it is now broken.

So it is kinda doable with the workaround as long as you keep it as a Simplified field notation, but this issue is very frustrating.

How can fields work correctly in one document, and not in another? Docs seems to have same setup, in same program and on same computer. Adobe, please fix this!