As soon as the new $100 bills were used in casinos, casino slot attendants who make handpays and casino cage workers and tellers were already complaining about the new bills and urging casino patrons to handle the bills carefully.
The problem seems to be that the paper stock appears to be thinner than with other US currency. I handled the new bills when I received a handpay at Harrah's Rincon Casino on Sunday night (see the photo below) and frankly I agree that the new bills appear to feel "thinner" than other currency. Because of the thinner paper stock -- and maybe because of all the features and the ink on the bill -- the bills also seem to stick together.
I saw casino workers spend extra time separating the bills in order to count them out to players at machines and at the cage.
When I had the bills from a handpay I also found that it was difficult to count them and to separate them.
However, the bills do work fine with the bill acceptor devices on slot machines and early this morning when I deposit some of the new $100 bills into a Bank of American ATM that accepts cash, the bills were accepted without any problem. I was careful to make a precise count of the bills before I put them into the ATM deposit device, and the machine and I had the same count for the deposit.
So it appears that technology accepts the new bills even if the paper does feel thinner and for humans the bills seem to stick together.
Perhaps as the bills are used the "stickiness issue" will resolve.