Why is my serial communication slower on a different computer?

I'm making a software to communicate in serial (over USB) with multiple (4 to 5) external devices. Some device are connected through a USB 3.0 hub. I use polling to get some data from each devices with 3 polling (of ~8-10 Hz) per device except one who has only one (slower) polling (~3 Hz). I set that if I don't get a value after a time (generally the delay between each query, ex: 125 ms), I ignore the missing value as it can happen. If there are too many consecutive timeout I consider that the connection is broken. Sometimes, the software will also send a different query (not polled) with a lo

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