Timeout crash on snapshots

When I opened server from 1.12.2 until 18w21b the server was opened.My friend try to connect with hamachi but he can for this reason:"an existing connetcion was forcely closed by the remote host".

When he try to open own server and connect its work fine but to my server its make a problem,he tried to connect other servers on this version(18w21b) and this work.What can I do with this we tried to update java,increase ram of the server etc. Anything won't work.

from the log:

[10:11:45] [User Authenticator #1/INFO]: UUID of player xBllue is 6762859c-617d-461e-9ee6-b98d6f9b4933
[10:11:45] [Server thread/INFO]: Name[/*] logged in with entity id 370 at (-281.0750563602533, 64.0, -75.68351018836682)
[10:11:45] [Server thread/INFO]: Name joined the game
[10:12:01] [Server thread/INFO]: Name lost connection: Timed out
[10:12:01] [Server thread/INFO]: Name left the game