'09 Electra, in semi mode, continues to fire after I stop walking the trigger

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Hello,

Did quite a bit of searching on the internet and on this forum specifically to see if anyone had this problem and came up with nothing. Here's my problem:

I've got an '09 Electra. Always shoot in semi, walk the trigger for speed. Occasionally, when I stop walking the trigger, the marker continues to fire as if it's ramping. It'll last anywhere from 1-4 seconds. It's super annoying because a. the marker is essentially out of my control, b. I don't want to be ramping or doing anything like that in a game, c., it wastes a ton of paint.

I have no clue what's causing this. I'll list the stuff I've got on/in the gun that may be pertinent:
Regulator: stock
Bolts: stock
Board: stock
Striker spring: highest (red) tension Trinity (although my gun did this before I swapped the spring out, I believe)
Battery: Spyder's 9.6v battery
Tank: HPA, Guerilla air aluminum w/ Myth
Hopper: Evo 3 w/ Z-board

I recently replaced a pinched o-ring in my reg, otherwise I regularly oil the striker o-ring, ASA o-ring, barrel o-rings, etc. I enjoy cleaning the gun so I do it after each weekend of play.

Any help would be appreciated. I'm thinking the board would be the first thing I'd eliminate by swapping it out temporarily (or buying a new one).

Additional note:
I'm missing my trigger's post travel adjustment screw; the gun did not ship with one. That's a separate issue but it could be related.

Thanks,
Mike T.