I have one interogation about the player’s UUID. When i’m logging in the server, my UUID is c583560c-d2ff-3102-b0b6-885d7d24a094, but my client give me 90d389a8-f979-40dc-b559-5ce44ffa9852. If you go on https://api.mojang.com/users/profiles/minecraft/djxy the id is 90d389a8f97940dcb5595ce44ffa9852(This is the UUID without the lines).
Server give me: c583560c-d2ff-3102-b0b6-885d7d24a094
Client give me: 90d389a8-f979-40dc-b559-5ce44ffa9852
Mojang api: 90d389a8f97940dcb5595ce44ffa9852
If the server gave you c583560c-d2ff-3102-b0b6-885d7d24a094, then it’s in Offline mode. Meaning the UUID was generated from your username, and not the server.
The client and Mojang API gave the same result, but the Mojang API removes the dashes.
In your server.properties is the key online-mode's value set to false? You don’t want this unless you have the need to remove the built in auth for special circumstances (which is safe to assume you don’t have?).
Visual: http://prntscr.com/7qherf
EDIT Ninja’d by @FerusGrim 
Thank you, it was the problem.
To solve the problem you need to change the online-mode in the server.properties at true.
Mind marking the thread as [SOLVED] in the title and posting an edit with the solution to the problem in the OP? This helps people who may have the same problem find the solution quicker.
Don’t know why I did this but here ya go
$ python -c "import uuid,md5;print(uuid.UUID(bytes=md5.md5('OfflinePlayer:djxy').digest()))"
c583560c-d2ff-f102-f0b6-885d7d24a094