The mausoeum map reverted back to the way it was when I started playing about a month ago. There is no way backwards/forwards, so one gets permanently stuck. Below is a screenshot with map, to help:
https://imgur.com/a/IH0B7uf
Point A used to have an exit to the graveyard. Point B used to have an exit to let you go backwards into the mechanical angels area (sorry, don't remember name of maps).
Thank you to DM Spartacus for rescuing me!