Unusual instances happening all the time (9)
I believe the answer is:
incessant
'happening all the time' is the definition.
(never ceasing)
'unusual instances' is the wordplay.
'unusual' is an anagram indicator.
'instances' anagrammed gives 'INCESSANT'.
(Other definitions for incessant that I've seen before include "Perpetual, unremitting" , "Continuous" , "Constant, unremitting" , "Since Stan was continual." , "Endless" .)