Check your trigger, safety and sear for slop or walking. I saw a video where a guy added a few small shim washers in his trigger group to keep everything "tight" and in line fixed his issues. If the sear and disconector drift apart slightly you can have a non reset.  Also remember a issue with the safety walking out causing  reset problems. Another fix was to add a overtravel stop to the trigger, if the trigger was pulled fully to the rear the disconetor would travel to far forward and the tab timing would be off. Check to make sure you have good spring tension on your sear too. Just some ideas from things I've read over the years. If it's a tab rest issue you would have to pull the carrier fully back and chamber a new round. Your issue sounds trigger group related.

Has anyone tried this modified disconnect or instead of tabbing the carrier? VZ.58 modified disconector

CarnageRush   I too have one  like that .