Full output of /ess version
[11:40:57 INFO]: Server version: 1.14.4-R0.1-SNAPSHOT git-Paper-154 (MC: 1.14.4)
[11:40:57 INFO]: EssentialsX version: 2.17.1.17
[11:40:57 INFO]: Vault version: 1.7.2-b107
[11:40:57 INFO]: EssentialsXProtect version: 2.17.1.17
[11:40:57 INFO]: EssentialsXGeoIP version: 2.17.1.17
[11:40:57 INFO]: EssentialsXChat version: 2.17.1.17
[11:40:57 INFO]: EssentialsXAntiBuild version: 2.17.1.17
[11:40:57 INFO]: EssentialsXXMPP version: 2.17.1.17

Server Log
Latest server log is 2 weeks old and not inherent to the problem.

EssentialsX config
https://gist.github.com/MartinLestrange/9c0cc0c308c66ad0323ad141937a1ed8

Problem
The command to spawn in a player head returns as: "Error Unknown item name" It does work in singleplayer and from searching the web I noticed this problem is connected to EssentialsX. If not then I'm sorry to waste your time.

What I have tried
/give @p minecraft:player_head{SkullOwner:"MartinLestrange"} 1
That one worked in singleplayer
/give @p playerhead{SkullOwner:"MartinLestrange"} 1
/give @p 397:3 {SkullOwner:"MartinLestrange"} 1
/give @p player_head{SkullOwner:"MartinLestrange"} 1

Edit:
Extra info: I have essentials chat disabled via my server hosting front end.
Extra Info: I recently switched from EssentialsX-2.17.1.0 to EssentialsX-2.17.1.17 to fix a different problem. It did still work in the previous version.

SOLUTION:

I got the solution through the discord server.

/minecraft:give @p minecraft:player_head{SkullOwner:"MartinLestrange"} 1

Essentials requires the "/minecraft:give" instead of simply /give.

Thanks!