When I updated my server today, I joined it and I was at the spawn, without inventory. I checked the console and I saw these messages:

[12:13:43] [Server thread/INFO]: Starting Minecraft server on 77.111.255.139:25565
[12:13:44] [Server thread/WARN]: Could not lookup user uuid for 37cb7f73-4cbd-4658-80e6-19a6f55fb73c
com.mojang.authlib.yggdrasil.ProfileNotFoundException: Server did not find the requested profile
at com.mojang.authlib.yggdrasil.YggdrasilGameProfileRepository.findProfilesByNames(YggdrasilGameProfileRepository.java:90) [minecraft_server.jar:?]
at pe.a(SourceFile:57) [minecraft_server.jar:?]
at pe.a(SourceFile:353) [minecraft_server.jar:?]
at my.aF(SourceFile:426) [minecraft_server.jar:?]

Whenever I restart the server, I'm teleported at spawn, my inventory is wiped and I see this message. I found that the .dat of all the players were still there, in a "playerdata" folder, while the "new" data are in the "players" folder. The inventory, xp, and the rest are still there too, I can see them with a NBT explorer when I open the old files. I tried to copy / paste my old data file into the players folder, didn't work. Renamed it so that it has hyphens between parts of the UUID (the old files have no hyphens while the new have hyphens), didn't work. If I take a dirt block, left, then join, it's still there, but if I restart the server, pooof, it disappears. I'm sure there's a workaround because I saw no other people having this problem.

Note : sorry for my bad english, it's not my native language.