tmi does not entirely adhere to the IRC standard, and as far as I know do not handle incoming PING’s. Only PONG [server] as a response to PING.
I could not see where the library responds with PONG’s, but I believe your problem is that you are disconnected when the library attempts to PING.
Either make it timeout after a very long time or scrap the library entirely. I made mine from scratch, and it’s not that hard tbh.