Ok, I've reviewed enough that I can make a general statement.
If you see a repeated "in transit" notification on your tracking number, over the course of several days, your item is still at the last processing facility mentioned. The "in transit", is because the system assumes it is in a trailer, going to the next processing facility. When it mentions the plant name and location, that is when the container your parcel is in was physically scanned by someone. This was never an issue before, as packages are normally sorted in less than 24 hours, then sent on their way. So, if it hasn't gotten to the next plant in the time that a truck would take to drive there, assume that the package is waiting to be processed, and we will do our best to get it to you as soon as possible. Air cargo space seems to have been freed up, as I was getting priority Mail boxes from fairly distant in the last few days, and they were pretty much on time.
YMMV, my experience in the greater Philly area.