I am not sure how long it has been going on for, but around 2 weeks ago I noticed my standard mob farm was not producing any goods.  I finally realised the minecart had stopped.  I started it again, but didn't wait to check it was going round, went to AFK and no goods.  I didn't see any mobs dropping and assumed it wasn't working anymore.  Roll on two weeks, I tried to fix the farm but couldn't.  Then I went to my Iron / Guardian farm today to discover that minecart had also stopped, fixed it and didn't think any more of it.  This evening on a livestream I discussed the issue, went to the Mob farm and realised the cart had stuck again and I could not make it move - as though the rail was switched off.  I removed the side blocks, the rails, replaced and made sure the powered rail was powered, I even added more in, but nothing worked.  It then occurred to me, that the other farm in a different location had stopped working for the same reason.  I have some screen shots for you.  They are both in chunks and do not cross over.  They have both worked brilliantly for the 10700 days I have been in the word with no issues until now.   I did check the other logs and they seem to be different and resolved.  I think one was works as intended and the other in spectator.  I couldn't find another ticket.  Thank you CJSGOOSE.

Images show both farms - minecarts are stuck.  A sequence is shown where I manually push the cart back and it works until reaching the same sport and stopping again.