3.2.1 usb problem

after install of ardu copter 3.2.1, no problems, except when i plug in usb, i get low battery warning and no -joy on mission planner connect (actually was able to connect one time, post update, to calibrate compass,)
can still access mission planner with 915mhz.

Hi There
Just wondering how did you sort out your issue as I have the same one when powering the pixhawk from a dedicated battery and BEC but through the output (SB)
Thanks for your help