In the past you could sometimes come across the deity Lolth being spelled 'Lloth'. I once heard it was a typo that somehow kept being repeated.
Where did the spelling 'Lloth' first appear?
Blame R.A. Salvatore.
Lolth was represented in several D&D Works, from 1978 to 1987. The discrepancy arrived with the Crystal Shard in 1988.
It was later corrected in Exile, with reason given
Drizzt quietly recounted to Belwar the story of the [...] decision to forsake his kin and their evil deity, Lloth. Belwar realized that Drizzt was talking about the dark goddess the deep gnomes called Lolth, but he calmly let the regionalism pass.
It has since been cannonized that while Lolth is the correct global spelling, the citizens of Menzoberranzan and Uluitur use Lloth.