Here is the documentation for the RECONNECT command:
Twitch IRC processes ocasionally need to be restarted. When this happens, clients that have requested the IRCv3
twitch.tv/commandscapability are issued a
RECONNECT. After a short period of time, the connection will be closed.
In this circumstance, please reconnect and rejoin channels that were on that connection as you would normally.
What does “a short period of time” mean? Due to rate limiting, it may takes some time to rebuild a connection AND join all channels, so I would like to know if this short period of time is 5ms, 5s or 5min.
I guess this is what determines the maximum amount of channels you join on a single connection, and the size of your connection pool.