Filtering by dates comparison

I am trying to connect Gmail with google sheets and in particular I am updating in the google sheet the date of last interaction via email.
To do that I am trying to compare whether my new email record is older that the record in the database. And this is where issues start:
Even though timestamp in Gmail is in standard format (and correspondingly in google sheets also, as they are populated originally through email timestamps) simple comparison of Time operators: Less than/More than 21.Timestamp produce somehow random results. Sometimes they are correct, sometimes not. But even if I cover them in parseDate( and parseDate(21.Timestamp) still produce random results.

What puzzles me the most is that Make correctly represents the date when I do debugging and point at the proper value - yet the comparison would still be incorrect.
Any ideas what could be an issue?

We would need some more information @martiran . Screenshots help a lot.
Anyway, take a look at the variable and check if its text or date object, if text look into the parseDate() function.