I have this problem only in one list and I don't know why.
I have create a list with many column. Most of the column should only be visible if a checkbox is selected.
So I used:
=if([$HAT] == true, 'true', 'false')
HAT is the name of the yes/no-checkbox field.
If I create a new item in the list, everything works as expected: see Screenshot "NewItem".
But if I want to edit an item, I get only a blank screen (no fields at all are visible) and I also cannot modify conditional formulas (menu does not open): see screenshot "EditItem".
If I don't maintain a conditional formula, editing a item works without a problem. If I now try to maintain a conditional formula for the same column while in edit-item mode, I cannot save the formula. The "save" button don't react. No error message appear: see screenshot "EditItem_CreateConditionalFormula".
I also already tried to recreate this list via saving a template and recreate it, but the error still appears.