When you try to edit a Reddit comment in their mobile web app, it deletes all line breaks from your comment so you have to remember to manually put them back before submitting.
The other big issue I have is that when you type in and edited comment, it will omit spaces between words at random. JFC, there's no reason to use anything but a vanilla HTML input element (because only markdown formatting is supported), but they somehow fucked up basic text input anyway!
My last little gripe is that nothing in the interface tells you that markdown is supported, which is extra dumb because the desktop interface tries so hard to hide the fact that markdown even exists.
(And yes, there are a host of other annoyances, but I'm trying to limit my criticisms to things that can only be explained by incompetence.)
I know that feeling well.