Here is the next sentence from "Tri b˙ada Catha Maige Rath":
IS e fath arna buaid suibni geilt do dul re geltacht .i. arar facaib do sgelaib + do laidib ac oirfid caich o sin i le
The corresponding passage in E1 goes:
+ nocan ed-sin is buaid ann suibni do dul ar geltacht, acht ar facaib do scelaib + do laidib dia eis i neirind;
A is much more abbreviated:
et Suibni i ngealtacht, acht is ar a mhed du laidib duroni;
Again my suggestion is to follow the lead of E2. "arar" in "arar facaib" seems to me corrupt and has to be emended, but maybe Charles could give it a try first of all.