I play Bedrock Edition on the Switch and when I place and write text on a sign in a Realm the text disappears. I also can't name items using an anvil in the Realm. I tried both of these things in a single player world and the text appeared fine which leads me to believe this is to do specifically with Realms. 

Unfortunately, I can't seem to figure out how to screen record on my switch to show this... Let alone how to send the files but it's very simple to recreate so I didn't think it was too much of a problem.