I'm seeing essentially the same problem since installing 220.127.116.11.
Like you, I'm converting from DVD to a .mkv file (xvid and audio pass through). So far every disk I've tried since installing this beta (several disks) starts converting normally with fps in the mid-50's. But somewhere around the 50% to 60% mark, fps starts dropping, and either just prior to or at 100%, fps drops to 0 and it never finishes. Clicking "Cancel" causes DVDFab to go unresponsive.
I'm following the same procedure I've been using for several weeks now without any problems until now. I'm going to try "downgrading" to the most recent previous version I have and will report the results.
Oh...and when I post the results, if someone hasn't opened a thread for this in the Mobile sub-forum, I'll do so at that time.