Found this out recently and think it may help those who encounter greyed out options or non working "Fly" button in MSFS. Acronis Cyberprotect and other modern backup solutions have a built in anti ransomware component. For some reason when the flightsimulator executable is downloading the game files it will delete the files in certain folders while leaving the folder structure intact. Funny thing is, when loading, the sim will see the folders and think all is well even though no files are in the nested folders. This results in missing components and MSFS not downloading the missing files no matter how many times you restart.  I have noticed this happen with navigraph manual installers as it seems all those text files in the addons navdata folder being replaced triggers the cyber protect ransomware mitigation (installing navdata via the apllication has no issues though). The kicker is, Acronis does not give a pop up alert it is doing this. You actually have to log into the Acronis management page and read the logs to catch it. After adding the exe's and folders to the allowed processes and exceptions list and deleting the empty folders in the MSFS official folder, the sim downloads the missing components once started.

Hope this helps someone, especially with crappy DSL like me who can't put aside a whole day to re download 100GB of files every time something acts up. What is odd is that Bitdefender EDR has no issues with either the sims or addons but the backup program does. Oh well. You live and learn.

thank you

Thank you for taking the time to warn us about that. Appreciated. 

This should be moved over into the MSFS Tricks and Tips Forum.  It is a good one.