I have a weird behavior on my xubuntu machine and I don\'t know why.
Mine was caused because I was using a keyboard layout different from English US (I could notice strange symbols when I typed in the emulator settings screen - the three dots as OP pointed out). After I changed my keyboard layout the problem is gone.
You see, the main case is Android Emulator Window don't have the proper focus even when you click on it. Yes, you can do any touch-operations, but frame still appears non-focused.
I've found a workaround for that:
Now, whenever you hang your cursor above the emulator window it'll gain correct focusing state and you'd be able to use you keyboard just fine.
If you open the Window Manager Tweaks menu and go to Focus tab then you can select the Do nothing option under the When a window raises itself. This worked for me multiple times. (Different ubuntu verions)
On Ubuntu 18.04 and 19.04 this happens when you have multiple keyboard layouts installed on your system. Try to select your first keyboard layout from the list to make virtual keyboard work in emulator.
Strangely, it doesn't matter which particular layout you have selected, or if it matches with language in the emulator, but looks like it is related to the position of the keyboard layout in the list.