I run into the ODM not working due to the new php7 mongo driver as a fool. I think that it must be alerted on the documentation. Any project using Mongo ODM with phalcon will not work with the new phalcon 3.0 There is an incubator adapter but all the mongo code must be rewrited (new Bson type instead of arrays, no MongoId, no MongoDate, etc etc...) so it's a big refactor if you are making use of mongo.
It will be good to alert the users about this issue on the blog.