for others with this issue, I solved it on OSX thanks to this page: www.silabs.com/community/interface/forum...0x_usb_to_uartb-LJMf

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As discussed in the following thread, it appears the v5.x SiLabs driver is completely broken.
Fortunately the v4.x driver, which is included in the "Legacy MacVCP Driver" folder in the same download, works fine. Do note that you might have to install it twice for it to work, as the first install will just remove the existing driver. If it's installed, there should be a "SiLabsUSBDriver.kext" file in /Library/Extensions with a date created of June 16, 2017.
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