I was entering new m3u urls for in the "TV source" area and it would not get to the keyboard. I downgraded to 2.40.2 and fixed it. I was having this problem on Fire TV 4K stick, Fire TV cube, & mibox3. I also tried the beta with no luck.
I'm guessing this is a bug.
I've tried the beta and it has the same issue. I'm surprised you are not seeing it because it has problems on 3 different devices for me. I am able to see the keyboard appear and disappear (real fast) in some instances and then I can't get it back, so I'm not able to enter any url.