My data validation isn't working in Excel 365. I guess there's a bug.

Nishkarsh31 

Allow me to say that it's amazing that the drop-downs worked at all (even sometimes). Downloaded your schedule and experienced the same problems. Your formulae can be easily avoided if you assign Named Ranges to your data validation lists. The Data Validation formula can then be as simple as "=indirect(cell)". I've reworked your schedule in the first 15 rows of the "Expenses" sheet to demonstrate how this works. First, I removed all your data validation and re-entered ones based on Named Ranges for the second level drop-downs. I expect that these will work all the time. Just be ware that Named Ranges only accept letters and underscores ("_"). But I'd rather use that than overly complex formulae that try to mimic the same functionality but don't work properly.