Hi, I’ve also found the CM3 to be more difficult to be discovered by RPIboot using same setups where the CM1 was 100%. You might try using a powered USB hub between the media stick and the host computer (and short, low-resistance cable between media stick and hub). Sometimes rebooting the host PC has helped in my experience.
If you (or others) would like to help me investigate this area, please send me an email (dave.chew@wdc.com) and I can send some hardware- CM3, media stick, CM-to-SATA adapter, short, low-resistance USB cable, etc. The raspberrypi.org forum might also have info, but I haven’t checked yet.
Thanks.
