Hello @charles,
Thank you for posting on the Startech.com Community!
I am sorry to hear you experienced some issues with PEXUSB3S42 in your PCIe x1 slot, though I am happy to hear that it is working consistently in the x16 slot. If the card is functioning properly in one slot but not another, then it sounds like the issue could be something with the slot itself.
The main suggestion I could recommend is checking in your computer’s BIOS/UEFI settings to see if there is an option to set the x1 slot to a specific PCIe version rather than letting it be set to autodetect. This setting is not available on all systems and unfortunately there is not a consistent name for the setting I could suggest to look for, but we have seen this setting help in some situations where PCIe cards are having detection issues so it may be of some help if it is available.
If this setting does not help or is not available, it may be best to continue using PEXUSB3S42 in the PCIe x16 slot.
If you experience any further difficulties with PEXUSB3S42, I would recommend reaching out to our technical support by phone or live chat here: StarTech.com Support
Lukas T