How many ports is licensed for this system? Also, is this seen only under a certain load or can happen with very few calls (if so for either how many)?
It appears there could be some breakdown in communication of internal components between messages passed between host library and firmware via driver. Hard to say though without having full logs, at different layer to identify the issue. I would also check debugangel output as well to see if anything prints during this timeframe. That can be enabled by installing the debugangel service from DOC prompt: debugangel -install
Jeff