Problems unchanged about drink being knocked back (7)
I believe the answer is:
enigmas
'problems' is the definition.
(enigma is a kind of problem)
'unchanged about drink being knocked back' is the wordplay.
'unchanged' becomes 'same' ('same' can be similar in meaning to 'unchanged').
'about' means one lot of letters goes inside another.
'drink' becomes 'gin' (gin is a kind of drink).
'being knocked back' is a reversal indicator.
'same' enclosing 'gin' is 'samgine'.
'samgine' reversed gives 'ENIGMAS'.
(Other definitions for enigmas that I've seen before include "'Mysteries, riddles (7)'" , "Puzzles - mysteries" , "They're mysterious or difficult to understand" , "'Puzzles, riddles (7)'" , "Problems" .)