These hub actuators are not a very robust design from Ford. On the Raptor forum, we refer to them as IWE, integrated wheel end. The IWE works with a spring and a vacuum. When the truck is running, the vacuum collapses the spring to disengage the hub. Of the is a leak in the vacuum line or the vacuum line valve fails, the IWE will engage prematurely.
Another issue is that the material Ford uses. The IWE ring teeth are made from plastic. Under 4x4 load, they can easily bust. I pretty much break one on each offroad trip I do. I've learned not to stress them if I can help it. I also now carry two in my offroad kit. Guys have gotten so good at changing these on the trail, I've seen it done in as little as 15 minutes.
So, it is not a surprise that you've had to have the driver side done, and now the passenger side needs it as well. Did you say the vacuum valve was changed previously?
@Yukon Joe