I have a non-functioning Roam. When placed on charging base, or charged by USB, there is a solid orange light for 10-15 seconds which then disappears.
I’ve tried the holding of the power button for 15 seconds thing a number of times, on and off the USB and the charging base.
The Sonos app recognises its disappeared but can’t find it again. No tones indicating being turned off or on again have been apparent. Rest of system functional.
I can’t be certain, but it may have been left off the stand long enough to drain the battery. I’ve left it for long periods on the charging base, and also by USB-C. No joy!