I have a similar issue and was directed here by Bortus from Minecraft help. I am playing on Switch. My kid and I are online at the same time but Minecraft Dungeons says not that my kid is not online in my friends' menu. Also, my kid tries to add me as a friend and the gamertag search says No Match! The Switch clock is set correctly and synchronized to the internet and does not resolve the issue.
I have a similar issue and was directed here by Bortus from Minecraft help. I am playing on Switch. My kid and I are online at the same time but Minecraft Dungeons says not that my kid is not online in my friends' menu. Also, my kid tries to add me as a friend and the gamertag search says No Match! The Switch clock is set correctly and synchronized to the internet and does not resolve the issue.