All players were suddenly kicked off the server

[2006lev-Web]

Hello, could you tell me what the problem might be? All players were suddenly kicked off the server, and an error message appeared saying: 'The server is not using a database'.

[13:34:48 INFO]: Sasasaco issued server command: /spec
[13:34:52 INFO]: Sasasaco issued server command: /reveal
[13:34:54 INFO]: Sasasaco issued server command: /reveal
[13:34:55 INFO]: Sasasaco issued server command: /spec
[13:34:57 INFO]: Sasasaco issued server command: /spec
[13:35:27 INFO]: LenChivatell lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client LenChivatell
[13:35:27 INFO]: LenChivatell left the game
[13:35:27 INFO]: zorooowww422 lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client zorooowww422
[13:35:27 INFO]: zorooowww422 left the game
[13:35:27 INFO]: svftqngel lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client svftqngel
[13:35:27 INFO]: svftqngel left the game
[13:35:27 INFO]: AutoMata11 lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client AutoMata11
[13:35:27 INFO]: AutoMata11 left the game
[13:35:27 INFO]: Golybuka712 lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client Golybuka712
[13:35:27 INFO]: Golybuka712 left the game
[13:35:27 INFO]: Itd_ lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client Itd_
[13:35:27 INFO]: Itd_ left the game
[13:35:27 INFO]: 2006lev_ lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client 2006lev_
[13:35:27 INFO]: 2006lev_ left the game
[13:35:27 INFO]: Igroman4cik lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client Igroman4cik
[13:35:27 INFO]: Igroman4cik left the game
[13:35:27 INFO]: TTyZaTuk lost connection: Disconnected
[13:35:27 INFO]: [voicechat] Disconnecting client TTyZaTuk
[13:35:27 INFO]: TTyZaTuk left the game
[13:35:27 WARN]: [Plan] Database queue size: 500, dropping some unimportant transactions. If this keeps happening disable some extensions or optimize MySQL.
[13:35:35 INFO]: UUID of player svftqngel is a0bfafef-ddcf-3c31-97cd-c0fdc788607e
[13:35:35 INFO]: UUID of player Igroman4cik is 546d529a-d23c-3f24-a8c8-aa0d1d05fdb3
[13:35:36 INFO]: svftqngel joined the game
[13:35:36 INFO]: svftqngel[/94.29.11.172:1092] logged in with entity id 448788 at ([world_nether]42.01846807004744, 130.1661092609382, -71.47447692145987)

Plugin versions
Plan-5.7-build-3306.jar

[AuroraLS3]

Something caused players to get kicked (not Plan) which then caused an influx of database transactions, so Plan reacted to try quickly reduce the queue by saying
WARN]: [Plan] Database queue size: 500, dropping some unimportant transactions. If this keeps happening disable some extensions or optimize MySQL.

This is normal behavior to avoid the queue becoming so large it would cause out of memory crash