I suggest taking a look at your html sanitization settings make sure html isn't allowed in markdown settings.
Next step would be to move the other 2 topics from that category and check if you still see broken markup.
Just noticed few vulnerabilities flagged by npm audit.
It may make sense to update less, debug (socket.io-adapter-mongo), and string.
Not sure however if updating these libraries break other code.
Thank you @julian , that's awesome!