Outflow valves begin to drive towards closed and slightly pressurise the cabin once above 65kts ground speed which is then usually followed by a EICAS should the valve fail.
Sounds like an intermittent fault as others have said which is enough to latch the EICAS & CMC. Swap the AC motor at least to find out if it's a AC motor fault or not.
If they poster is not a pilot I don't believe they should be participating in running checklists, so glad they did not get involved.