playback skipping in Pro Tools 12 [SOLVED]

[markparris]

Pro Tools 12. Audio tracks skipping during playback. I've just upgraded to PT12 and playing back a mix previously created from PT10. Strangely, the acoustic guitar tracks are skipping but not the vocals. I have bypassed all plugins. This made no difference. I have opened some other sessions and same issue occurs during playback.
Mark
ProTools 12.3.1, iMac Intel i7 16GB RAM late 2015, El Capitan, RME Fireface 800

[ronwasserman]

Create a new temp test session. Import JUST the ac guitar tracks. Do they skip now?

Also, in the master session, do they skip in the same place every time? (Probably not, but just wondering.)

[dr_daw]

I would do a disk repair and FULL shut down and restart.

[sw rec]

Recording to a separate drive?

[markparris]

I really appreciate this idea. The imported gtr track into a new PT12 session worked, so I reopened the original session and imported the track alongside the original. The new import also worked, BUT, when I copied an izotope plugin into the new track, you guessed it!!, the issue was back. Interestingly, I had bypassed the plugin originally thinking that may have been the issue but it made no difference. This time I opened the plugin and discovered it needed to be re-authorized. Conclusion!! the plugin reverted to demo mode!! All good now :)