Server crashes unexpectedly under minimal load

Server started not to keep up and suddenly crashed.

[20:29:36] [Server thread/INFO]: Wawua lost connection: Disconnected
[20:29:36] [Server thread/INFO]: Wawua left the game
[20:29:53] [Server Watchdog/FATAL]: A single server tick took 60.07 seconds (should be max 0.05)
[20:29:53] [Server Watchdog/FATAL]: Considering it to be crashed, server will forcibly shutdown.
[20:29:53] [Server Watchdog/ERROR]: This crash report has been saved to: /home/ondrej/minecraft/18w22c/./crash-reports/crash-2018-06-05_20.29.53-server.txt
[20:29:53] [Server Shutdown Thread/INFO]: Stopping server
[20:29:53] [Server Shutdown Thread/INFO]: Saving players
[20:29:53] [Server thread/INFO]: Vilecek lost connection: Server closed
[20:29:53] [Server thread/INFO]: Vilecek left the game
[20:29:54] [Server thread/WARN]: handleDisconnection() called twice
[20:29:54] [Server thread/INFO]: Srshen_mine_SVK lost connection: Server closed
[20:29:54] [Server thread/INFO]: Srshen_mine_SVK left the game
[20:29:54] [Server thread/WARN]: handleDisconnection() called twice
[20:29:55] [Server thread/INFO]: Sebukator lost connection: Server closed
[20:29:55] [Server thread/INFO]: Sebukator left the game
[20:29:55] [Server thread/WARN]: handleDisconnection() called twice
[20:29:55] [Server Shutdown Thread/INFO]: Saving worlds
[20:29:55] [Server Shutdown Thread/INFO]: Saving chunks for level 'world'/overworld
[20:29:56] [Server Shutdown Thread/INFO]: Saving chunks for level 'world'/the_nether
[20:29:56] [Server Shutdown Thread/INFO]: Saving chunks for level 'world'/the_end