I am not with Laminar Research; just a flight simmer.
Unless you have made a backup of the old version before you updated to the current 11.20 version there is no going backwards. Refer to others with the same problem in this forum within the last week or two.
In the meantime attach a copy of your log.txt file so others can have a look to ascertain what may be causing your problem. The version of the log.txt file should be immediately after you shut down or you "crash"