Don't know if it's at all related, but I'm working on a similar problem.
AC3.3 for TradHeli. When flying in Auto, with the Failsafe_Throttle set to "Continue if in Auto" and it is flying in auto, the motor output switches off briefly when the RC Rx comes in and out of range. It seems that this only happens if the Telemetry is also lost. I haven't been able to isolate the condition, I don't know if it's while flying in Auto only, or what.
Just several people pointed me at your issue as maybe being related.
Does Solo use the Motor Interlock function?