You’re in good company. I regularly check tracking, looking at packages that have been on the road for 5 to 10 days. I find that at least half have some irregularity.
Sometimes it does not get recorded as delivered; sometimes it does not get recorded as being dropped off by me; sometimes it magically jumps from a sort facility on this coast to the customer’s mailbox on the other coast without visiting any sort facilities in between.
I’ve had packages delivered with SC, but never received the sig.
I currently have a box in limbo someplace in the US. It was shipped to me from S Carolina 19 days ago. Last tracking info shows that it was in a sort facility in SC just a few dozen miles from the sender. Neither the sender nor I have received any notice from the USPS.