server closing on its own after joining.

me and my friends have a minecraft rp server that we were building in, but suddenly we were kicked. it said on the screen ''server closed'' none of us were the website closing it. we tried everything but it didn't work. the console log is right here ;

[23:29:38] [Server thread/INFO]: Starting minecraft server version 1.12

[23:29:38] [Server thread/INFO]: Loading properties

[23:29:38] [Server thread/INFO]: Default game type: SURVIVAL

[23:29:38] [Server thread/INFO]: Generating keypair

[23:29:38] [Server thread/INFO]: Starting Minecraft server on *:45275

[23:29:38] [Server thread/INFO]: Using epoll channel type

[23:29:38] [Server thread/INFO]: This server is running CraftBukkit version git-Bukkit-9a1fc1e (MC: 1.12) (Implementing API version 1.12-R0.1-SNAPSHOT)

[23:29:42] [Server thread/INFO]: Preparing level "world"

[23:29:46] [Server thread/INFO]: Preparing start region for level 0 (Seed: -7727923094707181940)

[23:29:47] [Server thread/INFO]: Preparing spawn area: 1%

[23:29:48] [Server thread/INFO]: Preparing spawn area: 33%

[23:29:49] [Server thread/INFO]: Preparing spawn area: 73%

[23:29:50] [Server thread/INFO]: Preparing start region for level 1 (Seed: -7727923094707181940)

[23:29:51] [Server thread/INFO]: Preparing spawn area: 67%

[23:29:51] [Server thread/INFO]: Preparing start region for level 2 (Seed: -7727923094707181940)

[23:29:52] [Server thread/INFO]: Preparing spawn area: 4%

[23:29:53] [Server thread/INFO]: Preparing spawn area: 11%

[23:29:54] [Server thread/INFO]: Preparing spawn area: 19%

[23:29:55] [Server thread/INFO]: Server permissions file permissions.yml is empty, ignoring it

[23:29:55] [Server thread/INFO]: Done (13.076s)! For help, type "help" or "?"

[23:29:55] [Server thread/INFO]: Starting GS4 status listener

[23:29:55] [Query Listener #1/INFO]: Query running on 0.0.0.0:45275

[23:29:58] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 2557ms behind, skipping 51 tick(s)

[23:31:00] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 10519ms behind, skipping 210 tick(s)

[23:31:01] [User Authenticator #1/INFO]: UUID of player billiexoxo is fb5f92d4-1f29-4494-967d-65657469fb83

[23:31:02] [Server thread/INFO]: billiexoxo[/50.100.196.18:50885] logged in with entity id 276 at ([world]282.2893310257712, 72.59568889376162, 191.16787311240873)

[23:31:11] [Server thread/INFO]: billiexoxo issued server command: /time set day

[23:31:11] [Server thread/INFO]: [billiexoxo: Set the time to 1000]

[23:31:47] [Server thread/WARN]: billiexoxo moved too quickly! -7.4864843086842825,6.562910713341196,2.9731095335266673

[23:31:48] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 23938ms behind, skipping 478 tick(s)

we dont want to lose everything we did, does anyone have a way to fix this?
we only had two plugins which were world edit and colour signs, and now when we look in plugins (files), they are deleted. no one deleted them.
( i made everything that said ''server thread/WARN'' bold and italic )