[Mashiro]

The problematic rule that you isolated is rate limiting connections to port 7777. It limits the port to 6 connections per second on port 7777 with bursts to up to 12 connections per second globally (meaning all possible connections to that port). And I would easily assume that generally when you connect or others connect there are way more than 6 - 12 connections being opened up on port 7777. So well... you get kicked out because the firewall gets triggered exactly through that problematic rule and terminates all new connections.

limit

This module matches at a limited rate using a token bucket filter. A rule using this extension will match until this limit is reached (unless the '!' flag is used). It can be used in combination with the LOG target to give limited logging, for example.
--limit rate
   Maximum average matching rate: specified as a number, with an optional '/second', '/minute', '/hour', or '/day' suffix; the default is 3/hour.
--limit-burst number
   Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5.