Most likely the plug caps have loosened on the on the coil wires.
Try tightening them, if they will not tighten then remove the cap and cut the mandatory 10mm off the wire and refit the cap
I did check them when putting the new plugs in, they seemed quite "in place" to me, with no movement.
And i don't touch the plugs until i need to renew them if all is well, so it's not like they get yanked about.
I'm wondering if i've got a bit of dirt in a carb needle that's letting just that extra bit of fuel slip by, causing the momentary explosion.
It's annoying, 'cos the bike has been running beautifully since i changed all those parts and did a carb balance, it's been like riding a new bike so to speak. Starting instantly, faultless RPM needle movement at tickover, accelerating and pulling hard through every gear, it's been a pleasure to ride, not that it's ever been bad though.
I might try a cheat and give it a bit of the old STP Fuel Cleaner treatment and see if that might dislodge or clean anything, i haven't used that stuff for quite a while, but it's done good things in the past.