Air Traffic Controller reported incorrect lost communication procedures being utilized by UAS in Class A airspace. This led to the target dropping off the scope and caused confusion and safety issues for ATC.

Narrative

Aircraft X is a drone that is supposed to transition from R-XXXX to Location with prior coordination. There is a specific procedure that is supposed to be followed when this happens. To start; the pilot did not file the flight plan correctly and it had to be entered by the controller working R-XY/XZ as we were taking the sector in order for the drone pilot to transition out of R-XXXX and to Location. About halfway through the sector; the drone pilot did several radio checks in the spot where he usually loses comms. He could not hear us on mains/standby or BUECS (Backup Emergency Communications Systems). He could temporarily hear us on the Guard frequency. He then lost comms entirely; but did not follow Lost Comm Procedures. Instead; he changed his squawk code; which cause the tag to go into coast track. This caused the tag to time out and drop completely [from] the scope while the drone was still in our airspace. We noticed and started a VFR tag for him; since he was now just a Mode-C intruder in Class A airspace. He seemed to change his mind; squawked his original code; then changed his mind again and went back; which again caused his datablock to go into coast track. This is incredibly dangerous; and had we not noticed we could have easily climbed or descended an aircraft through the drone. Recommendation - The drone pilot should consider reviewing Lost Comm Procedures. Had he squawked 7400 as he was supposed to; we would not have lost a tag on the drone.