I believe the problem is the dates. I configure the column to accept dates as MM/DD/YYYY.
In manual transaction the date is correct. After being insert the MM and DD are swapped.
As you note, it seems likely that the problem is a result of changing the date format/locale. Someone from Tiller would need to confirm because we can’t see how the manual transactions and balances are added.
The Balances sheet shows the amount from the latest Balance History row for each account. If you correct the dates on the the Balance History sheet, the Balances sheet should correct itself.