There is no doubt that people have been having issues with the Avid Video Engine in Pro Tools 11 and 12 and so Avid have produced an Avid Video Engine Report form that you can fill in outlining your issues.
We have reported here many times about the Avid Video Engine which was completely overhauled in Pro Tools 11. Anecdotally we have also heard reports that people are staying on Pro Tools 10 because of the issues with the Avid Video engine in Pro Tools 11 and above. On the other hand we have also heard reports of people happily leaving Pro Tools 10 behind because the Avid Video engine has resolved the problems they were having with video in Pro Tools 10.
Lets help Avid by reporting all the problems with the Video Engine using this form and please be constructive and helpful and give as much information about the issues you are having so that we help Avid make Pro Tools even better, by fixing the issues that really bug us.