I get this error message "fatally missing registry entries" when I try to join a local server I set up. I've narrowed it down to Quark or Forge.

I have a test server set up using forge-1.12.2-14.23.0.2515 and the only mod is Quark-r1.3-112 and AutoRegLib-1.3-14 (everything is the latest, MC at 1.12.2). In single player, the mod works fine as intended, but when I try to join the multiplayer server, I get the "fatally missing registry entries" error and can't join, the server says player joined then disconnected. I've tried the recommended build of Forge (not latest) and i've tried previous versions of Quark (all for 1.12.2) and no combination will work in multiplayer, just the same error.

No extra mods, everything default, new worlds after each attempt, nothing I do seems to work. (I have also setup another local server with 9 mods that have no issues with latest forge, but once I add Quark, it throws up the error upon joining. So now I'm using the above test server to narrow down the issue.)

Let me know what more you need.

which logs? There are 4 .log files in the server logs folder.

I made a gist (first time) and have the 4 logs.
"deleted log"

Anything in your client? Doesn't appear as if the server logs are any help.

Sorry, here you go, just ran a fresh set. Same error still.
"deleted log"

[00:36:58] [Netty Client IO #1/FATAL] [FML]: Failed to connect to server: there are 10 missing registry items
[00:36:58] [Netty Client IO #1/DEBUG] [FML]: Missing minecraft:entities Entries: [quark:wraith, quark:ashen, quark:dweller]
[00:36:58] [Netty Client IO #1/DEBUG] [FML]: Missing minecraft:potions Entries: [quark:curse]
[00:36:58] [Netty Client IO #1/DEBUG] [FML]: Missing minecraft:blocks Entries: [quark:ender_watcher, quark:iron_rod]
[00:36:58] [Netty Client IO #1/DEBUG] [FML]: Missing minecraft:items Entries: [quark:ender_watcher, quark:iron_rod, quark:soul_bead, quark:trowel]

This appears to be your issue. Make sure your quark config on the server is the same as the one in the client.

For the client, it's in your instance dir, /config/quark.cfg. You can get there ingame by going to the resource packs menu, opening the directory, and going one level up.

For the server, it's in your server root, same location.

Just copy the file over and override the one you don't want.

Thank you so much! That was exactly the issue, the two configs were slightly different. I configured the client config ingame, but didn't think about the server config.

Fixed!, you can close this ticket. Thanks again!