Glass panes, fences, iron bars and cobblestone walls sometimes fail to upgrade

Are you able to attach your world or a test world (from 1.12.2) to reproduce the issue?

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.

The world in question is of the wrong version. It is of 18w07c.

If you have a 1.12.2 world which has issues upgrading please reopen the ticket.

All places mentioned in the description look perfectly fine since the last snapshot.

Please re-open with a world/position to teleport to with a repro case if this is still happening.

This bug is back in full-force in 18w22a. Confirmed by loading several backups of older worlds (mostly 1.12.2). Nothing at all is connected. Fences, gates, iron bars, glass panes etc. Cobblestone walls become invisible with no collision box, as if they don't exist at all. Stairs also exhibit some "connectivity issues", especially corners.

They only fix themselves with a connection update. Block updates alone don't suffice. Placing a non-connecting block next to it has no effect. Stairs don't update. They have to be broken and replaced.

See MC-130140