Error when trying to parse date in format "yyyy. MM. dd.": "invalid formatting code: unsupported or unescaped characters"

[jerbob92]

When trying to parse an XLSX sheet with the date format yyyy. MM. dd., the following error is returned:
invalid formatting code: unsupported or unescaped characters

Here is the sheet I'm trying to read: https://www.mnb.hu/Root/ExchangeRate/arfolyam.xlsx

I'm not really sure if yyyy. MM. dd. is an actual valid date format, but LibreOffice shows the dates fine. Could it be that the . only has special meaning following some formatting characters?