Initial h before I, n, r disappeared in ONorw. at a preliterary date but was regularly retained in Olcel. (cf. Noreen §289). In Olcel. this initial h - was often lost, or an initial h - was often added to I, n, r, through association between words having initial hl, hn, hr and words having initial l, n, r. This associative process was due to resemblance in meaning or in form aside from the initial consonants in question. After the loss or the accretion of initial h - had become established between certain words or word groups there developed a general feeling of uncertainty as to whether a word should begin with hl or l, hn or n, hr or r . Most cases of this type of general confusion are naturally found in the Late Olcel. period, yet several instances may be cited in the classical period; which shows that the process was even then well under way. For the classical period I may mention the following examples: Hniflungr (Elder Edda) for Niflungr, rār ‘damp’ (Elder Edda) for hrār, hrjā for rjā ‘wrestle’; for the Late Olcel. period hnezla (for nezla) ‘button loop’, hniᵭra (for niᵭra) ‘to lower’, reᵭr (for hreᵭr) ‘genitals’, hreifr (for reifr) ‘glad’, hrifsa (for rifsa) ‘to rob’, ringja (for hringja) ‘a round pail’.
Albert Morey Sturtevant (Thu,) studied this question.