DENIED
As this is a warning appeal, rather than a staff report, I am upholding the warning and denying the appeal. Based on the video evidence you provided, it shows you close a door, the researcher in question then opens it, requesting you kill them, to which you state is referring to the D-Class on the other side of the door. At no point does the video show you telling the researcher to not open the door, explain your low health, or take any other action than just blasting the researcher with your shotgun.
Proper action in this instance, if he were endangering you, would have been to express that, order the researcher to step back, attempt to handcuff the researcher, and then shoot them. Jumping directly to shooting is improper, and failing to follow an order from a MTF member is not a valid reason for an immediate KOS.
On a side note, you're more than welcome to put in a staff report using the clips you sent to my DMs via discord while I was at work, however I find zero evidence to support any sort of staff bias charge against the admin in question. The final decision for that is obviously not up to me, but just my two cents.