Well, I can't replicate exactly that but I have serial devices connected to StellarMate and still no issues. Try to swap ports, or check power supply. (now running 35 mins with 5 devices connected to StellarMate and still no timeouts)
I tried all of that over the course of a couple of months. Different USB-cables, different powered hubs, non-powered hubs, exactly the same behaviour running kstars natively on my macbook pro and on Linux Ubuntu virtual machine on my HP-laptop. But everytime I get the same results. So I'm pretty out of options by now. The only thing left to do I if there's no solution for this is to get a new guide camera maybe. Any suggestions on what is a good reliable option?