MAX(values) doesn’t work properly in the scenario where you rollup a date field which uses formatting. It’s no longer recognised as a date and can cause problems.
It also looks like old field level formatting is stored when a datatype changes. I used an existing field that was formatted for currency and changed the formula to simply show a date field. My rollup in the parent record caused a major problem later on although the child field appeared as it should: I was locked out the parent table as it got stuck on the ‘Loading’ screen.
To re-enable access to that table I had to change the formula in the child table.
Hey folks - I came here hoping to find a solution to this bug that I’m also experiencing. Unfortunately, it looks like one does not yet exist, so I had to build a bit of a workaround. Check it out here - while this certainly isn’t ideal, it solves the problem of finding the latest (or ‘max’) date.
Oddly enough, this also seems to work with rollup fields, although I can’t for the life of me understand why. (Even though Airtable tells me the the rolled-up date field — which it displays in ISO-8601 interchange format; e.g., 2018-11-13T00:00:00.000Z — is not recognized as a date, seemingly it is a valid input to DATETIME_FORMAT().)
BTW, the 'x'format specifier causes DATETIME_FORMAT() and DATETIME_PARSE() either to return or to expect a date expressed as a Unix timestamp. I increasingly make use of such in Airtable, as doing so avoids a myriad potential pitfalls owing to mismatched or region-specific formats.