I’m experiencing the same issue with the “Repair Vehicles” Challenge, it’s progress being stuck at 142/2,000.
In addition to that, some of the verbiage is vague in the Challenge Descriptions. One example being Tier 1 of the “Rapid Fire” Challenge under the Weapon Challenges. Both of the descriptions read “Inflict Damage With Assault Rifles”, however the number values are significantly different and track differently, despite appearing identical. Some clarity on Challenge Descriptions such as this would be a welcome change.
Overall there’s not too much else I noticed. Loving the game so far!