Southern Wyoming. Amount of pressure has been crazy this year. I'm able to hunt every day of september and this is the third year doing so, nearly 20 years hunting this area. My notes from last year said that on the 16th there were 2 camps with people in the area, this year, that number is 20+ and doesn't matter if it is a weekday or weekend.
1st - 4th, was crazy. Summer herds were still breaking up and all the bulls were acting like peak rut. We are talking running in to multiple 50+ herds bugling constantly from sunrise to noon. 5th-18th things are nearly totally silent and most elk have pushed off. I have a suspicion that they have gone to limited quota units which, while happens every year, the sheer number of elk that seem to be gone is rare. Run in to small herds (1-6) almost every day though nothing is talking. Lone cows with spikes, groups of 6 cows with no bulls, groups of 2-4 bulls hanging out, All absolutely silent. All people i've run in to have anecdotally also reported the same thing (minus the limited quota suspicion).
I strongly suspect that a large part has to due with the hunting pressure which is several times what i've noted in any previous year. However, summer herd breakup typically happens mid august, not early september. So, some chance there is a degree of lateness on activity due to that.