We have two Kindle Fire Devices that cannot connect to realms. On the Worlds tab, there is a message that says "All Reams have been updated. You need to update your game to continue playing Realms." 

I do not have this problem with Minecraft on Win 10. I can enter the realm fine. 

One difference that I notice is that on the Kindle, the version listed on the splash page is v1.14.21, whereas on Win 10 it is v1.14.20. The Kindle app was updated on 1/30/2020, whereas Win 10 was updated on 1/28/2020.