I am using the Windows Client of Trello 2.11.5 but was able to reproduce the following issue in desktop but not in Android app 2020.8.14111-candidate.
Note the following card:
Then notice what happens to 1 2 and 3 after you save:
If you edit the comment the numbers then show up correctly so it would appear to be something about the the content is being parsed that is transforming the value for display vs. actually changing the content that is saved. Not sure how to turn this into a ticket as it seems like something that needs to be addressed.
Can any test on Mac and iphone and confirm if this is happening there?