Again, just to cover all bases. You said you ran the engine in conventional. So, from that, we believe the engine is not mechanically jammed or binding. Yes, under conventional the voltage would vary but, that same voltage is what determines the commanded speed, so it's less likely to invoke the safety condition for locked motor and thus cab light blinking.
However, any command mode operation- bluetooth, TMCC, or Legacy, the engine assumes and expects to have plenty of source voltage headroom for the motor to be able to achieve the commanded speed under load. And this is where users can get tripped up. Either just from old engines not complaining in this state or the user just unaware of how and why this could get invoked. The manual warns about too high of voltage (anything over 19V) but doesn't warn users that too low of track voltage or power loss, dips, bad track, could invoke the safety when running in any of the forms of command mode.
