2017 Volkswagen GTI engine issue

Hi all,

Looking for possible solutions here.

About a week ago, I had a misfire in cylinder #2. No noise, no CEL.

Did not drive the car for 5-6 days, until my appointment for spark plugs / coils.

Yesterday, had new plugs and coils installed. They’re saying that when they removed spark plug #1, the tip wasn’t there… they replaced all 4, and the coils, cleared the codes and went for a test drive.

They came back to misfires in cyl 3 and 4, and a knocking noise.

They’ve got no rough idea of what it could be, and want to bill me ~15h of work to diag.

Does anyone here have any clue of what it might be (other than a new engine) and if it’s worth pursuing fixing or if I should move on.

Thank you all in advance,