The slime's spawning rate are extremely low on the Beta version , Although it has been fix in the version 1.2.13 , but it has not been fixed in the beta version.
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[Mojang] Mega_Spud (Jay)
migrated
 i can confirm this for the xbox one as well i cant seem to find ANY slimes
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-21856.
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