Said to be missed due to poor visibility (4)
I believe the answer is:
mist
'poor visibility' is the definition.
(mist causes poor visibility)
'said to be missed' is the wordplay.
'said to be' indicates a 'sounds like' (homophone) clue.
'missed' sounds like 'MIST'.
'due to' is the link.
(Other definitions for mist that I've seen before include "Think fog or low cloud" , "Obscure" , "Watery vapour" , "Fine spray" , "Fret" .)