Discovered today 19.2.21
Windows update forced user settings to display region in a whole different country and the Windows data format for short date changed from (dd/mm/yyyy) to (dd MMM yyyy).
The format function used to format dates into a manor fit for SQL server failed. Format(date,"yyyy/MM/dd") resulted in the answer (yyyy MM dd) using spaces instead of backslashes. Once the windows setting was changed back to (dd/mm/yyyy) the error vanished. When trying to replicate the issue the regional settings would no longer allow the short date option (dd MMM yyyy) therefore we could not rhobustly test this error.