When starting to pedal, it takes half a rotation to "catch" While power pedaling on my mountain bike, when I coast for a second, it takes a half a circle on my crank to catch. Can anyone tell me the problem?
If chain us not slipping then id say you have a busted freehub by the sound of it.

Take the cassette off, remove the freehub inspect the paws check for excess grease or lack of.

Otherwise look at a new freehub body. I had the same issue you describe last week.