Timestamps are stored as floating point numbers in double precision, on the scale where 1 corresponds to a day. It is generally advisable not to test floating point numbers for equality; the rounding errors, inevitable in almost any calculation with them, may lead to unexpected results.
It appears that the transmission of time data from a form to the spreadsheet involved some sort of rounding of binary data along the way. Compare:
The number of zeros at the end of mantissa of the second number indicates that it was rounded along the way.
One solution is to use fuzzy comparison, for example
=filter(A76:A96, abs(A76:A96-B76) < 1e-9)
Since 10-9 days is less than 0.1ms, this matches the timestamps that are indistinguishable for practical purposes.
Another solution is to "fix" the distorted timestamp by converting the time to a string and back:
This will return the result identical to other 3:30 PM entries of your sheet.