I had this issue in the first few days of using 2021, there was also a short thread about a similar issue that I responded to around that time.
Most of my songs have a retard in the final 3 or 4 bars and I have loop on as default.
When looped the song did not revert to the original tempo but stayed at the last tempo set.
This had not happened prior to 2021.
As VideoTrack says the quickfix is to set your tempo in Bar1.

I reported this to support around Dec 8 and it seems to have been fixed in one of the new builds after this date.
Are you up to date with your build updates, we're currently on 813.

Vintage