Apps uninstalling on their own?

[AC Question]

I got my new Oukitel K6000 pro with Android 6.0 just a couple days ago and everything is great except one thing: everytime when I turn off or reboot my phone, firefox and poweramp uninstall on their own, and I have to reinstall them back. They don't just disappear from the homescreen, because even Google play tells me to install them. It happend 3 times already, and I couldn't find any info about it. Thanks for any help. PS: I also use an SD card.