I'm finding that can't get markdown (or even formatting using the toolbar) to work as expected.
I most often see this when writing a PR description and the problems are usually centered around code blocks and unordered lists:
For example here is what wrote in a recent PR description:

Here is what I get after I click Update Pull Request:

And this is a mild example, quit often all the bullet items have been concatenated on the same line and the code blocks look like long inline blocks instead of a solid block.