Ok, comparing the Amazon hardware with the Sparkfun hardware, the issue seems to be when scanning for the fx2lafw in PV (which my understanding is when the firmware gets updated on the device).
Both devices, when initially plugged in, are recognized by the custom name I assigned in Zadig. However, after selecting the fx2lafw driver in the “Connect to device” window in PV, then clicking “Scan for devices using above driver”, the Amazon device is rediscovered in Device Manager as “fx2lafw”, and PV works as expected. After following the same steps with the Sparkfun device, it’s rediscovered as “Unknown Device #1” in Device Manager, and PV fails with “Failed to open device, generic/unspecified error”.
Since I’ve seen no response here, I’ll proceed to RMA the product.