As a Gemini owner I can't say I've experienced any of these problems, though I have noticed a serious drop in battery life since the 8.1 upgrade. Also, occasionally the youtube app crashes the phone when switching away/back to it, which is to put it bluntly a bit of a pisser.
It's the lack of support from MediaTek that's the problem. They don't properly support their hardware with drivers kept up to date with the latest Linux kernel. You're dumped on ancient releases and no bug fixes, even the Android 8.1 update was a bit of a miracle.