Quoted from PanzerKraken:The 60th also probably took away resources if they are having to deal with licensing and if that's already a pain, they are having to coordinate two different products as well as approvals for two machines. As Gomez noted they got new music in 60th which is coming to the Cornerstone too, so they had to go and get that approved, so if it's taking a long time to work with the licensors then yea they are splitting resources.
Not so much them going slow, but probably having licensors telling them "no" on their ideas, forcing them to change and resubmit over and over. Then if there is problems with not allowing them to stack assets of different films, that probably was not in their original designs, so back to drawing board.
I think it's clear there is a serious unexpected roadblock with the IP holder
The 60th probably needed very little approval since there are no movie assets so cabinet/playfield art and music then they were off to the races with logo/animation approvals along the way.