I updated my kernel to kernel v4.18 on my Acer laptop with a AMD A12 and Radeon RX and it gave me all types of problems, went back to 4.15 and the problems stopped. I would try down grading your kernel to the default kernel and see if that helps.
I found it! The answer was yes, I was missing something. This is a gnome bound key combination to switch panels. I found the setting using:
gsettings list-recursively | grep -i Tab
and replaced it by using
gsettings set org.gnome.desktop.wm.keybindings switch-panels "['<Control><Alt><Super>Tab']"
Then, since Gnome wasn't overriding my ...
I'm making this an answer because I don't have enough reputation to comment.
This sounds like a memory leak. A good first step is to install and run htop to see if any processes are consuming quite a bit of memory. From the terminal:
sudo apt install htop
and then once you've installed it, htop. Once in htop, press F6 on the keyboard, and scroll down and ...