Facebook post engagement Ads not being delivered

Hi guys!

I've been trying to boost my fan page posts with no luck. Ads had been approved but there was no reach. I tried ads optimized for website clicks with the same creative and it worked like a charm, but I'm stuck with the post engagement ads, they're not being delivered to the audience. Any ideas why it could be happening?

UPDATE:
I've tried the same thing with another FB account for a different fan page. Post engagement campaign shows active status with no actual reach. Any thoughts...?