The server is closed when you join it. Modded

Server Discussion
1

When the server 1.12.2 is running without players, the ping goes steadily 0ms - 1ms, but if you enter the server, it will rise to 20000ms
logs:

2

You may want to read this

https://docs.spongepowered.org/7.4.0/en/server/spongineer/incompatible.html