C. F. Keil and Franz Delitzsch on Jeremiah 33:8

Jer 33:8

This prosperity gains stability and permanence through the people’s being cleansed from their sins by their being forgiven, which, according to Jer 31:34, will form the basis of the new covenant. Regarding the anomalous form לכול for לכל־ rof לכול mro, Hitzig supposes that in the scriptio continua a transcriber wished to keep the two datives לך לעונותיהם separate by inserting the ו. But the form כּוּלּם, Jer 31:34, is equally irregular, except that there the insertion of the ו may be explained in this, or in some similar way.