Hi Chase,
Looks like its a time zone issues. Which timezone are you in? Looks your local time zone has DayLIght saving change starting on 01-Apr.
Try using trimToMonthsUTC , it uses the UTC timezone instead of trimToMonths which uses uses the user’s timezone
Regards,
Shekhar
In addition to Shekhar’s useful answer the steps for you. In the past I had also issues, so I think it’s useful to see those steps too:
trimToMonths($dt/DateTimeTester)
formatDateTime($dt/DateTimeTester, 'yyyy-MM-dd')
formatDateTimeUTC($dt/DateTimeTester, 'yyyy-MM-dd')
You see the difference between UTC time and session time (localised).