Same stuff happening since 11.01 (might be .51 update). Minecraft on Fire tablet stopped discovering worlds hosted on Windows.
What I've checked:
1. this is not a network issue, since if I run standalone bedrock server on Windows, android tablet can join
2. both Minecrafts have same versions
3. Windows version can discover and connect to the world running on Android
4. made sure settings "multiplayer" and "visible to LAN" are enabled.
5. checked firewall, minecraft has all the permissions (no changes made before the issue occured)
Dupe, same issue when Android MCPE-165950