What I did:
Entered preformatted text enclosed in backticks and then tried to change the format of text on subsequent lines to not be preformatted.
All text on subsequent lines were preformatted and would not change to other styles even when selected from the style menu.
What I expected:
I expected the style to change to that which was selected.
When I type text without the backticks and change the style using the style menu I do not encounter this problem.
Things that might be helpful to know (Agenda version, OS and model, etc):
Version 9.1, Mac OS 10.15.1, MacBook Pro (15-inch, 2019)
I experienced this problem prior to upgrading to Mac OS Catalina