Sometimes plugging in USB doesn't give ADB/MTP
Instead it simply falls back to the usb-moded
mass storage mode as seen in host dmesg
; I've had this happen a few times in a row but eventually when replugging enough times it finally gets detected in the expected mode(s).
Reproducible on latest 20.04 devel r572 where you'll see something like the following on host sudo dmesg -w
when replugging the cable a few times on the host end for example in case it doesn't happen first try:
[ 3452.434415] usb-storage 3-1.1.3:1.0: USB Mass Storage device detected
[ 3452.434503] scsi host6: usb-storage 3-1.1.3:1.0
[ 3452.434567] usbcore: registered new interface driver usb-storage
[ 3452.435977] usbcore: registered new interface driver uas
[ 3453.447109] scsi 6:0:0:0: Direct-Access Linux File-Stor Gadget 0419 PQ: 0 ANSI: 2
[ 3453.447217] scsi 6:0:0:0: Attached scsi generic sg0 type 0
[ 3453.458370] sd 6:0:0:0: Power-on or device reset occurred
[ 3453.459507] sd 6:0:0:0: [sda] Media removed, stopped polling
[ 3453.459691] sd 6:0:0:0: [sda] Attached SCSI removable disk