I have been in the swamp around 20 minutes and have not seen any slime, and also they cannot be spawn using the mob spawner.
PD: The problem is in the beta 3
PD2: I have a samsung galaxy note 4
MCPE-11413
Slimes are not spawning
Resolved
Duplicate
0
(Unassigned)
Unconfirmed
Tablet - Android - Samsung Galaxy Note
Android Lollipop 5.1
0.13.0 Beta 1
Retrieved
This depends on the type of moon that is present. "They spawn most often on a full moon, and never on a new moon"
Does this help your problem?