Offset keys can be for several reasons:
Check to make sure that your Comp frame offset and Mocha’s frame offset match. If there’s a different starting time between the two, the keys might get offset.
Also check to see if you have any time remapping on your layer. Mocha will ignore timestretch and work with the raw source material unless the layer has been precomped before applying the Mocha plugin.
When in doubt, always pre-comp your footage before you apply Mocha and make sure that the clip is trimmed in your pre-comp.