I use the official mobile app, and also use Apollo (because I like having two separate apps for two separate accounts I use).
The official mobile app is just inexplicably bad. The other day I was browsing through the 'Popular' tab, and every time I clicked on the thumbnail for an article, it took me to the web page... of some other article. Completely unrelated as far as I could tell. Tap on a CNN article about Trump indictment, instead get an EW article about Gwen Stefani (or whatever, I don't remember what it was).
It was consistent, too. Every article went to a different article instead, but tapping on that article always gave you the same different article. Tapping onto the comment screen and then onto the article gave the correct article.
A few weeks ago, the problem was different; I would tap on an article, and it would load up some other article, and then also the article I was trying to read. I'd read it, close it, then have to close the other article, then I'd be back at the main list.
For the longest time, refreshing an article list would result in a bunch of broken-looking entries in the list view; entries without titles, titles overlapping images, entries that were too big, and so on. Refreshing again often fixed it, but then gave me a new set of articles as if I'd already read the messed up ones it had brokenly tried to show me. This used to happen every single time; then it was just sort of random, about 50% of the time. I haven't noticed it lately because I got out of the habit of refreshing lists and I just kill the app when I want to get newer content.
There's also a little hovering downwards-arrow symbol to skip to the next top-level comment. It's black, it's fairly large, and it hovers over the content. You can't get rid of it whether you want it or not. The best you can do is toggle a preference that says "I don't want this to be movable", and then it sits in the corner, over top of the content, forever (except when it bugs out and sits in the middle of the screen on the left side forever).
For the longest time, the comment box to type your comment into was a fixed size; if your comment didn't fit into two or three lines, then your text wrapped onto the fourth line or whatever, except the text box wouldn't scroll so you couldn't see what you were typing. I got in the habit of copying the text to Notes, writing my comment there, and then switching back to Reddit. 50% of the time, the Reddit app would reload and I would lose the comment that I was replying to, but the other 50% of the time I could paste my comment in and post it.
When creating a new post, you first put in the content you want (title, body, image, whatever), and then you hit 'Next' and choose a subreddit. It gives you a list of suggestions, based not on subreddits that you're subscribed to or post to regularly, but rather subreddits that you've engaged with lately. I saw a post from /r/doordash yesterday, so now the app is suggesting maybe I want to post there, or /r/Weddingattireapproval.
Note that some subreddits don't allow self posts, or don't allow image posts, but you have to create your post first before choosing a subreddit that maybe doesn't allow it, forcing you to go back and change your post type/content. This feature seems just generally really stupid.
It goes on and on. It's a genuinely horrible app which can rarely even get the basic functionality working, and bugs stick around indefinitely.