I think that is very risky business splitting an RS-232 signal. What is the requirement for this? What product are you connecting to?
Does your end device work when connected via this splitter and only one ConnectPort?
The splitter is not a straight through device as you can see from the pin outs: Pins 3,4,5,7, and 8 connected straight through between the MASTER and PORT 1-n. Pins 1, 2, and 6 “diode ORed” from PORT 1-n to the MASTER port
I would be mapping out the pins to see what is going on.