Hi

The only reason I can see for the default audio device to change would be if you lost connection to your usb audio interface this would throw you back on the internal sound card.
Possibilities are poor connection. Poor quality, or long usb lead, or over aggressive usb power saving scheme.(set usb ports to never off in your scheme which should also be set for high performance.)

Mike


BIAB2021 UltraPlus,AsusN55S1Tbssd, W10/64,Akai EIEpro
Yamaha CVP405,SquireStrat, CoolsoftVMidSynth
Novatation Impulse61 Ctr kbd, Cwalk blab Kontakt

http://mikesmusic.byethost16.com/