It's often the case with AAA productions that require the existing workforce to be supplemented for a time, and was always likely in the case of Avalanche Studios, with the developer wrapping up Mad Max and the imminent Just Cause 3. As confirmed by Game Informer, the companies' two offices (Stockholm and New York respectively) are being impacted by job cuts, with around 20 people losing their positions.
Expecting to hire more in 2016 and promising to take measures in order to avoid this situation in the future (and noting that some developers are being rehired in Sweden), Avalanche Studios explains that, "in starting up our new projects, we were not able to perfectly match the team sizes and skill sets of the previous ones, and we unfortunately had to let some talented developers go."
Besides, it's the first time that the developer has been involved in the release of two high-profile open-world action games in the same period of time, and with that in mind, the studio's contraction isn't really that unexpected. We wish those who've lost their roles at the company a speedy return to work.