Appears to be resolved as of this morning, everything is back to normal.
Similar issue on PC (UK).
Finished playing at ~01:30 GMT this morning, at which point my milestones were 91% complete:
Campaign 23/23, Arcade 21/21, Multiplayer 29/29, Troopers 83/91, Heroes 86/100, Starfighters 44/50.
Logged in again ~13:00 GMT, at which point the milestones were 33% complete:
Campaign 0/23, Arcade 0/21, Multiplayer 2/29, Troopers 9/91, Heroes 61/100, Starfighters 33/50.
Re-starting has not resolved the issue.
Like @grimmace2 most of the "incomplete" milestones show "complete" progress (e.g. 10/10), but are not greyed out and therefore not registering as complete.
However, the "Unleash Your Anger" Arcade milestone and the "Starting Assault Training" Troopers milestone show complete reversion to 0 despite having been completed previously.
Interestingly, the progress towards all the milestones I am genuinely still to complete displays accurately. I know this because I have some of my key stats, including milestone progress, recorded in my own Excel spreadsheet.
