Forced Subtitles no longer working

Only by making it appear to Plex as completely new. (by performing the Plex Dance )

Which then also affects the ‘Added at’ date of this item and makes it appear as ‘Recently Added’ in the user interface.
Manually pre-selecting the right subtitle stream using the web app might be easier.

Keep in mind that the subtitle selection (manually or automatically) is stored per-user-account.
If you are concerned about your shared user getting the right subtitles selected by default: as long as they haven’t touched the subtitle selectors, they will get the forced subtitles automatically selected.