I agree they shouldn’t have just relied on the oximeter...just had to deal with complaints/MDRs too much in my line of work....(20+ years of med device)
After spending the end of my engineering career packing up manufacturing plants for shipment I totally feel your pain.
Kindest evaluation I have of Far Eastern manufacturing processes is the fabrication is okay but Quality Control sucks.
Particularly electronics. (Unless you're an Apple supplier and are forced to throw away your junk before you ship...)
(I'd hazard a guess that your complaints/MDRs amounted to 25 - 30 percent of available stock....)