We were able to fix our cook errors with the help of an Epic dev on the discord channel who looked up the actual server cook error from our job number.
It turned out to be several level sequences. We then narrowed that down to a track in each of the sequences where we were animating an object that attached to the bone of a animated rig using an attachment constraint. Once we removed that track, the cook errors went away. Not sure why, maybe constraints in sequences are not fully supported yet?
But more importantly, this took our project down for the last 3 days. And all that really needed to happen was for the server to show the actual cook error in the output log. This would have saved us many wasted hours. Please, please fix this.