I have tried two other IRC clients on the iPad Pro, exactly the same bad result.
It is as if the Pi either has developed some stateful association with the first iPad, the iPad 5, maybe by source address, or else it just does not like having two simultaneous SSH connections. mind you, in the second case, I don’t know why the first connection would not have timed out possibly, but you could get locked out forever like that, just because you change IP address, which happens a lot, especially with IPv6, and of course with mobile machines, machines that are multihimed, or roam to 4G or umpteen other things?