Do you have a barrier nearby?
It could also be that bench that is blocking. Have you tried removing it?
Sometimes when an object that can not be passed by guests is placed nearby something that has an animation, it despawns those guests at the end or during their animation.
Try placing a bin in a crowd. Most peeps will disappear and spawn at the park entrance.
You can place a barrier in front of a shop. The guests will still use the shop but despawn as soon as they start leaving the shop.
I believe this is new, as soon as a guest get's "stuck" it teleports to the entrance.