I haven't played Destiny 2 for a few months now and all my progress from Forsaken has been deleted, what can be the reason and could you fix it?
It was announced in the weeks before the big 10/1 update that uncompleted campaign progress would be reset. This occurred because the campaign structure was converted from Milestones into a Quest-based campaign step system. You can re-start your Forsaken campaign from the Director map of the Tangled Shore. Along with that, if you desire, you can also redo the Destiny 2, Curse of Osiris, and Warmind campaigns by gonig to speak to Amanda Holiday in the Tower.