Subscribe to a scenario from the Steam workshop. Perform any kind of save except "save and exit". If you're affected by the issue, the only way to recover that save is to rename it continue.Arma3Save. Because if you relaunch the scenario from the beginning, the game erases all the gamesave files and therefore cannot be loaded from the escape menu.

– autosave.Arma3Save are autosaves during the mission and also created with the script command save().

– save.Arma3Save is the manual save via the escape menu.

– continue.Arma3Save is created by the command "save and exit".