I think I know the answer to this but I want to clarify. When Cell Portal takes you back to the first ICE, do you then have to encounter all the ICE again?
I would say not due to the rule "The runner approaches the outer most ICE that has not already been approached this run".
However does Cell Portal override this and effectively start the run again?
There is no such rule in the rulebook. The exact quote from the rulebook is:
"A Runner approaches each piece of ice protecting the server one at a time, starting with the outermost piece. The Runner must PASS each piece of ice in order to approach the next piece of ice protecting the server, continuing until all pieces of ice have been passed or until the run ends."
There is nothing about ignoring ice that has already been "approached".