Google Sheets UNIQUE not removing all duplicates

I have a table in which the headers should be all the unique start and end times that are in another table. However, when I use the UNIQUE function, the result still contains duplicates. Does anyone know why this might be the case?

This is the formula I'm using:

=TRANSPOSE(SORT(FILTER(UNIQUE(FLATTEN(B3:B,E3:E)),UNIQUE(FLATTEN(B3:B,E3:E))<>""),1,1))

As you can see, there are duplicate values for 04:00 and 05:00.

I've checked to make sure the values are all formatted the same way but I'm still getting this problem.

Here's the link to a spreadsheet with the problem.

Any help would be greatly appreciated.