As far as the pitch error I would definitely suspect IR2 since it provides attitude information to the F/o's PFD and hence on the gound I would most likely do a realignment. As far as part two of your question I had exactly the same experience two years ago on a CATI ILS and it was associated with the Collins Radio Altimeter. Did you arm the approach push button above 5000 ft on that approach?
Collins needed a modification two years ago because it did a self test at 5000 and if you armed the approach p/b prior to the self test (above 5000) there was the posibility of errors. However this mod has been implemented a long time ago. Chech what make of Radio altimiters are installed on your aircraft.