I'm not sure if this is the response you are looking for, but it may be interesting in case you always want to apply this formatting.
That is, the thousands separator being used by Tableau is dependent on the locale of the computer it is being used on, and then more specifically the workbook locale that has been selected. That means, if you select a workbook locale (through File > Workbook Locale) where the apostrophe is the common thousands separator, this will be applied throughout your workbook.
Here's an example where I selected German (Switzerland), where the apostrophe is used as well.
Hope this helps!
it solved my problem, thank you, however the explained strange behavior with the formatting is not cleared.
Still I accepted your answer as correct
Thank you again.