@harry_w Nope, the only mod I have that only affects the Arrow is a replacement for the prop animation. I use the "standard" Working Title Garmin upgrades, a UI modification (just changing the style and size of aircraft nameplates), a couple of realism mods for default aircraft (DA40-NGX, DA62X, JPL 152, HPG A5, WT CRJ), a handful of purchased aircraft, and the rest is scenery. Nothing fancy.
No idea what's going on, and so far the performance issues have not returned, in spite of adding more and more add-ons with every MFS restart. Fortunately, I recently discovered the "MSFS Addons Linker", which makes enabling/disabling add-ons rather painless.