Clearly related is the verbal root *ply ‘to delouse’ widely attested throughout Semitic.
Cf. Tna. ˁafäl ‘insects or fleas which live in grass’ (TED 1949). One wonders whether it could be directly compared to Akk. uplu (< *ˁupl-)?
Phonetically a very difficult case; diverse phonetic processes are likely due to different patterns of compatibility of root consonants in various languages.