The guttural nasal disappeared in an unstressed syllable when preceded by an n in a stressed syllable in the course of the OHG.
The cause of these double forms is in a great measure due to the two OHG.
The singular of nouns of this declension was inflected like the a-stems ( 42) already in OHG.
Before other consonants when followed by an or j in the next syllable, and further in OHG.
And owing to the weakening of the case-endings of the plural in passing from OHG.
This simplification of double consonants took place during the OHG.