-Minecraft 1.16.5
-Forge 36.2.21
-Testing Instance: Custom private instance with Eidolon and Eidolon Data Recipes installed (+JEI)
-Used Data Pack Loaders: KubeJS, Global Data & Resourcepacks
-Modfiles: jei-1.16.5-7.7.1.139.jar; eidolon-0.2.7.jar; eidolonrecipes-1.3.jar; globaldataandresourcepacks-1.16.5-1.10.2.jar; kubejs-forge-1605.3.19-build.258.jar
-Multiplayer affected (dedicated servers?)

Issue:
JEI wont show the modified recipes on server, if you start your game and join a server right away without joining a singpleplayer world before.

Tried different scenarios:

Scenario 1:
-Start Game
-Join server right away (without going into singleplayer before)
->Result: JEI shows default/unchanged eidolon recipes not the modified one

Scenario 2:
-Start Game
-Join Singleplayer world first
-Join server afterwards
->Result: JEI shows modified recipes

Scenario 3:
-Start Game
-Join server right away (without going into singleplayer before)
->Result: JEI shows default/unchanged eidolon recipes not the modified one
-Join Singleplayer world
-Ho back to join server
->Result: Result: JEI now shows modified recipes

So joining the singleplayer world before or after joining the server will fix this issue. But this has to be done after every new gamestart

Each scenario:
-in every scenario it was possible to craft the modified items, no matter what was showed by JEI
-modified recipes loaded with only KubeJS mod
-modified recipes loaded with only Global Data & Resourcepack mod
-both enabled
->All had the same result described in scenario 1-3.

(-Server and Client had the data pack installed)

From my testing this should be fixed in 1.4, please have a go when you get the chance

No issues anymore 👍