New roof install - plywood question

I just had a new roof installed and I noticed this oddity when the crew was doing the work. It looks like the plywood in the circled area is bowed and I can see obvious space between that and adjacent pieces of plywood. This piece of plywood was not replaced. I talked to the contractor and he said he is not concerned about this. Should I be concerned? He has offered to re-do this part of the roof, but said it will be "intrusive" and does not recommend it. Any suggestions?

the plywood is supposed to lay flat with a 1/8" space between the sheets.

IF the sheet is only spanning two rafters fix it the right way with a sheet of plywood that spans at least three rafters. Otherwise you could simply put a couple 2x4 or 2x6 under it for a little extra support. Chances are that there may have been some moisture that got in from the skylight causing a little warpage.

Yes, you need to concerned if you think that the issue is not resolved. You can talk to other roofing contractors about the problem for better advice.