This doesn't make sense
Last night I used the exact same set up, the exact same way, lined up scope and torch at 178 yards on a big rock I could see very clearly.
Scope mounted FandyFire STL V6 LED flashlight, mounted to a scope ring picatinny/weaver rail thingy by an adjustable mount.
On inspection it is throwing some light onto the arse end of my T8 can.
But, it had to be doing that last night too!
There is a difference in the weather tonight, in that there was a downpour, the mod was wet, there is also more moisture in the air.
But, remove the mod, problem gone.