no problems
‘No problems’ and ‘No problem’ are both acceptable phrases.
not an exact science
If you undertake an activity that is not an exact science, it will involve opinions, guessing, working with limited information, etc.
not having much luck
This phrase can be used in sentences such as ‘I have not been having much luck searching for my lost kitten.‘.
Not that I know of
The phrase ‘Not that I know of’ means ‘Judging from the information I have, the answer is no ‘. A variation of this phrase is ‘Not that I am aware of‘.