I was unable to recreate it with a very minimal test in a new 1.12.2 world, so I stripped out all the regions outside where the issue is and uploaded the world here:
Most of the issues can be seen in the house at 262, 92, 47. If I destroy and re-create the objects in question, they connect correctly, and sometimes replacing one piece of fence in a string of fence triggers all of them to connect.
MC-125625![[Mojang] Georgii Gavrichev](../../../data/avatars/users/22428.png){kind=small}
The world is too large to attach, let me see if I can trim it down some or create a test world.
Due to user stupidity I don't have the pre-upgrade world.
I was unable to recreate it with a very minimal test in a new 1.12.2 world, so I stripped out all the regions outside where the issue is and uploaded the world here:
https://drive.google.com/file/d/1Q6_AYudHkaKnC2NLKKmwBzWOi6ErdjWo/view?usp=sharing
Most of the issues can be seen in the house at 262, 92, 47. If I destroy and re-create the objects in question, they connect correctly, and sometimes replacing one piece of fence in a string of fence triggers all of them to connect.
Hopefully that helps.