Just wanted to share some recent experience- I suffered intermittent "no fires" from a Sako 75, (typically at ~30m with a roe or fallow eyeballing me, ain't that just the way).
Having chambered a round, the trigger would not respond, as if the safety catch was engaged, or as if the action had already fired.
Firing pin indicator would show action as cocked.
Round extraction would reveal a chambered round, no light strike indication, or very occasionally a very, very light strike.
Being intermittent the issue was a sod to fault find.
A bolt servicing didn't resolve the issue, but Peter Jackson of Jackson Rifles kindly and correctly identified the likely cause- a failure of the bolt security key lock. Apparently it does happen.
Resolution: a £15 repair from GMK which dispensed with the security lock feature, fine by me, would prefer to explain loss/theft of a rifle w/out bolt to the Police than "oh, but it's got this lock on it anyway Officer).
Hope this saves someone some teeth grinding