Connecting to a SMP Server running the latest 1.7.10-server version on a vanilla forge-1.7.10-10.13.4.1614 server does not work with some clients.
The following errors are logged:
Line 10069: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Limestone Slab Line 10120: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Mossy Smooth Betweenstone Slab Line 10136: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Weedwood Planks Slab Line 10225: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Mud Brick Slab Line 10234: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Smooth Betweenstone Slab Line 10330: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Solid Tar Slab Line 10441: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Smooth Pitstone Slab Line 10447: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Smooth Cragrock Slab Line 10503: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Rubber Tree Planks Slab Line 10805: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Cracked Betweenstone Brick Slab Line 10848: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Cragrock Brick Slab Line 10872: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Temple Brick Slab Line 10884: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Pitstone Brick Slab Line 11691: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Mossy Betweenstone Brick Slab Line 11795: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Limestone Brick Slab Line 11873: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Betweenstone Brick Slab Line 11986: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Thatch Slab Line 12041: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Weedwood Planks Slab Line 12672: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Limestone Brick Slab Line 12927: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Smooth Cragrock Slab Line 13409: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Solid Tar Slab Line 13644: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Limestone Slab Line 14301: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Smooth Betweenstone Slab Line 14453: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Temple Brick Slab Line 14738: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Cracked Betweenstone Brick Slab Line 15246: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Mossy Betweenstone Brick Slab Line 15550: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Cragrock Brick Slab Line 15572: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Pitstone Brick Slab Line 15947: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Rubber Tree Planks Slab Line 15978: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Mossy Smooth Betweenstone Slab Line 16291: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Mud Brick Slab Line 16453: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Thatch Slab Line 16708: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Betweenstone Brick Slab Line 16736: [19:36:31] [Netty Client IO #1/INFO] [FML/]: Found a missing id from the world thebetweenlands:Smooth Pitstone Slab

The same version of the Betweenlands mod works on another client.
Any ideas how to fix this?

Oh sorry, didn't and still can't find the "Creating Issues" Topic...

Yes I'm running forge-1.7.10-10.13.4.1614 on my server on top of vanilla server jar.
What I don't understand is that one client works perfectly and the same modpack on another client doesn't work with the errors above.

It's on the front page I linked, it's hard to miss.
If you have other mods installed, try removing some of them until the problem is gone

Oh man, sorry. found it :)
Did you make any changes to the Slab Registration? As it seems that all the slabs are missing in the one client!?

wrong button , sorry xD

Please read "Creating Issues" (on https://github.com/Angry-Pixel/The-Betweenlands) on how to properly write an issue the next time.
Since you didn't specify, I'll assume you're running a non-vanilla (vanilla as in the forge installed on the vanilla server jar) server which could be the cause of this.

Yesterday evening the client was able to connect to the server without any problem. Today the same problem again. Could you please give me any hint where to look or what to do? :/

If you have other mods installed, try removing some of them until the problem is gone

It's difficult to tell what's wrong because you're using a modpack and I can't reproduce this.

I'm sure you can remove mods. The point is to just temporarily remove them to figure out if another mod causes this problem with the BL

I can't remove any mods from the modpack... :(
But I can give you the link to the modpack: https://www.technicpack.net/modpack/survivorspack.926205 and the server IP via private message.

Ok nevermind, I removed the Betweenlands mod, as it seems to be a little bit buggy in the 1.7.10 version.