I'll start by saying that I already know some of you will say "I haven't had any of these issues", and that's fine and believable, but I'm just giving my own experience so I don't really care
First of all, the "Android TV" app for my phone, which is used as a remote, can NEVER connect to my box. Google's support website says to try it with Bluetooth instead of wifi, and it STILL won't connect for me (it will show my box on the list of available devices, though). I have tried the app with multiple iPhones and I was only able to use the app within the first month or so of me buying the Mi Box. This could very easily be an issue with the app itself, but it's still part of the Android TV ecosystem and it's worth mentioning. Plus the app is still being updated so it's not even a case of abandoned development.
In terms of the actual device itself, the YouTube app will always begin playing a selected video, but it will pause and show a black screen until I press Play again. Not a big deal, but an annoying inconvenience. Further, when I try to cast a video from my phone to my box, the Mi Box will close the YouTube app as soon as I minimize the app on my phone.
Moving on to the Hulu app, I'd say 70% of the time when I go to start a video, it will begin playing with a black screen, forcing me to back out of the video and begin playing it again. Luckily I can usually get it to play properly right away after doing this, but there have been times when it took a few tries.
Thirdly, there are times (although infrequent) in which NO APP will play a video. I go to YouTube, get an error on every video I try to play. I go to Hulu, same thing. Same situation for every streaming app I have installed. This persists until I reboot the box (which is a pain in the ass in and of itself, but that's not an actual bug).
Does anyone else have a similar experience? Perhaps it's all the fault of the individual apps' developers, but the last issue I mentioned definitely isn't. And even if it DOES fall on the devs, there's no excuse for it still happening after we've had these devices and apps for so long. Nevermind getting shafted by Xiaomi in terms of software updates (which I'm still pissed off about), but then we get shafted by the app devs too? There's no way I'm the only one having these issues, even if nobody who replies to this has experienced it themselves.
Overall the box is still a big convenience to me, especially since I no longer use an Android phone. But these little issues have been annoying the hell out of me just because there's no excuse for it. I know the box is relatively cheap, but these are not issues akin to the hardware not being powerful enough to stream 4K video, for example (that reminds me, my TV is only 1080p so the resolution shouldn't be the cause of these issues).
Despite the low price, the Mi Box is a disappointment given that it's basically abandoned by Xiaomi. Unfortunately the competition is 2.5x the cost. That been said, mine works well for what I use it for.