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.
Is there a way i can restrict the type of topics/post in a category?
like an pictures category where u can only do pictures (like instagram feed)
or a video category where u do only videos (like instagram stories)
then it showns in the homepage like this & people can scroll?