ישעיהו לב:י פירוש: רש״י ואבן עזרא

Year after year (lit., ‘days upon a year.’) Comp. (supra 29:1) “Add year to year,” and your sins are constantly becoming more serious, until eventually you shall be troubled, those who are now confident, for the vintage of the grapes shall be over for them, and the ingathering of the grain shall not come into the house.

שנה על שנה ═ ימים על שנה. Year after year.

the ingathering (אֹסֶף) This is a noun; therefore, its accent is on the first syllable and it is vowelized with a ‘pattah’ (now called a ‘segol’).