M600 PRO - all firmware updates up to date as of this thread started

1. GPS connection once all pre-flight checks completed - 17 satellites
2. Command to start motors initiated - motors will not start
3. "Invalid GPS Signature" warning message pops on screen, all satelittes lost
4. Restarted aircraft, issue went away.

No information on any forums about this issue. Any insight on cause and solution for this warning?

Nobody ever answered this, so her you go: if you get a used M600Pro and you're getting the "invalid signatures" you just update the firmware and it is done. This was solved in firmware version 1.0.1.60