Could the speed of processing have to do with the global entry center one is applying at?
No.
As it is explained to me, all applications are sent to our background investigators in VT. They all get divided up amongst the workers there, and it gets done when it gets done. This is why two people who apply at the same time, at the same computer, with the same information, will have their applications approved at different times.
On a local level, we only deal with applicants once conditionally approved. In person, people often ask us at the GE offices if we can do anything about their application. It sucks when mom shows up with her husband and 3 kids for their appointments, but we can't get her in because her application still shows "Pending Risk Assessment," weeks after the rest of the family was approved.
Also, due to the previous shutdown, our port is a few thousand interviews behind. There was talk about contacting those people and having them come in on a walk in basis, or even working weekends to get them caught up. Ultimately, the threat of a new shutdown has cancelled those plans, and now those people need to reschedule themselves online.