I can vouch for the flashes while the green line is up and it also knocks down fps every time it does.
I can only repeat and confirm the green line, but itself, is NOT causing fps nor flashes. It seems the problem is caused by the ENB series which, as tested with KLAX, is able to bring down fps A LOT, which is understandable, because KLAX use shaders a lot, and the ENB series does to and, GPU power is not an unlimited resource.
That green line in your video isnt the green line thats the issue in my case. Its the one that says its to wait while caching at the very beginning when you first go to an airport.
What you are describing is NOT the normal "green line" but, instead, is the RED text that is indicating GSX is updating its cache. It should appear ONLY if you added a new scenery, it shouldn't appear at every FSX startup.
If it does on your system, it means you have either a permission problem in your folder (running FSX As Administrator should fix this IF this is the problem) OR another FSX addon is keep changing .BGLs at every startup, forcing GSX to update its cache at every FSX start.
Nothing of this is caused by the normal "green line" texts, which are white over green.