Part 107 UAS crew reported during a training flight an incorrect switch was manipulated causing the UAV to make uncommanded movements. The UAS then had a lost link and impacted a field.

Narrative

I was PIC for the flight tests during the incident; with the aircraft used during this flight; which is a homebuilt prototype by the owning company (I work for). The aircraft was modified with radio control ability (a radio control receiver (RX)) for manual injection of a PIC actioned failure using a handheld radio control transmitter (TX); as well as for an additional operational risk mitigation to switch to manual attitude control mode; from automated control mode. This incident did not cause any property damage or injuries.During an automated mission takeoff there was an unintentional actuation of the incorrect transmitter switch. The intention was to use the failure injection switch command; though the unintentional action toggled the manual attitude mode takeover switch instead. The unintentional action caused personal confusion; causing the aircraft to make a ground impact; under power; and then climb at maximum throttle setting; without any control authority from the radio TX controller. After exhausting all control options at my disposal (manual and automated system) and knowing once switched to attitude mode there is no returning to automated mode; I stated I had lost control to the flight crew. The aircraft climbed to a point where it then shifted to descend and had an attitude controlled landing in a field. Upon aircraft retrieval onsite inspection; it was found that the radio control RX unit was disconnected from the leads to the flight controller; and damaged where the lead plugs into the unit. The initial ground contact is thought to be the cause of the RX unit system disconnect. Aircraft logs found that the maximum altitude reached was 1265.4 ft AGL. The aircraft maintained last commanded throttle input from the radio control; after the link was lost.The previous days/weeks leading up to this date caused higher stress levels to myself; and teammates. I believe this is a factor which helped lead to my temporary confusion causing the unintentional action.Mitigations have been reviewed and actioned into place:1) The aircraft flight controller system has an addition of an attitude flight mode Link Lost timer to actuate after a specific amount of time. This is in addition to an automated flight mode timer; already in place. The flight controller also now has adjusted throttle settings when a link is lost.2) The procedure to adhere the manual radio control receiver has been reviewed and improved; adding multiple layers of adhesion.I am confident this instance of a fly away risk has been mitigated.