I use reshade but dont use my own shaders. I do know that something changed with the graphics engine with yesterday’s patch which only happens when something has changed on the game side.
Try the following, go into window mode, start a flight, open reshade and turn on your custom shader, and then return to fullscreen mode and see if its working. This is what I have to do whenever there seems to be some whodoo being done the the graphics engine.
Of course it could also be something in your custom shader is wrong for MSFS. Just because it works on other games, doesnt necessarily mean it will work for MSFS.