The only CGT you will have sale of shares is if the shares derive the greater part of their value from Irish land. If you have bought standard quoted shares, which it sounds like, then you shouldn't have any Irish CGT. The only matter, on which I'm not sure, is if you have bought shares in an Irish REIT - I'm not sure if CGT applies there.
Your forthcoming return to Ireland won't have any issue on the your CGT treatment - you are still non-resident and non-ordinary resident.