Hi Steve, had a look at the logs, they look mostly normal to me, and if the ttyUSB1 stays that way I wouldn't bother too much, got some questions:
- do you have a so called eqmod cable? it seems pl2303 may look like one and the eqmod chip may cause problems on Linux (I recomment in fact using normal USB cables)
- are you running through a powered USB? The lines containing "over-current change" indicate that whatever device is there is requesting more current than the pi may provide. Can't tell for sure what kind of device is there, you may have more luck adding usb_max_current_enable=1 in /boot/config.txt

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