iPod shuffles not showing up in Music or finder

Hi, I have two shuffles for swimming and they're not recognized at all. I found this issue in another thread, and tried both solutions - safe mode and another user, but neither worked. I tried Disk First Aid (they don't show up), and turning off Apple Music as well. A few days ago one was working fine, and the other was still in the box, untried. I'd really appreciate any help as these cost $200 each, and another $150 taxes and shipping to get them to me in Costa Rica.. Thanks, Alex