UPDATE: Patch 1.2, released on 19th February 2018 fixed the issues with Milestones.
To address the many recent complaints from players the developers of Star Wars Battlefront 2 are releasing an update today or tomorrow. There have been reports of missing milestones and achievements. As a compensation all players will receive a bonus crate including 4000 credits and Standard Starfighter rewards.
Here’s what the DICE community manager said:
Our team is working to resolve an issue surrounding milestones/achievements not being granted to players who have earned them. The team has an update rolling out tonight that will address the issues players have been experiencing.
Alongside this update, we will also be granting all players a bonus crate, as we realized this issue had prevented players from earning their daily challenge rewards. The bonus crate will include 4,000 credits and Standard Starfighter rewards.
I have included this issue in the Star Wars Battlefront 2 Problems and Fixes master list.