Pressure or case defect or ?

Ok, so running a ladder with RL17 for 7mm08 with 150gn LRAB's Hornady brass.
First 4 loads showed no over pressure signs - primers slightly flattened but plenty of rounding on the edges still visible, and no marks on case head and no sticky bolt. 5th load ..... sticky bolt ... but when case ejected it was missing the neck.
Jagged separation at the neck/shoulder junction. See photo below.
All the the primers including this one from load #5 showed very similar degree of flattening, which was not by any means excessive.
Attachment 52037

I did not proceed with any hotter loads, the neck from the case came out clean when I pushed cleaning rod w brass brush thru.
So I'm looking for some advice - is this a case failure/dud brass (case was reloaded 4 x) & not related to over pressure ? Has any one else seen this ?
& thoughts on proceeding up the ladder by another 0.5 gn or so ?
Load #5 gave 2760 fps.

Yep seen it before on a 223 a mate had. He never annealed his cases and on the 5-6 loading they started parting company.
So I would say the neck has work hardened and needs to be annealed.

I would agree that the primers don't look flat so logically no high pressure signs.

Was wondering about annealing. Normally go 4 reloads ok before I bother with annealing but Hornady brass seems quite hard so perhaps more prone to work hardening.
Have seen Hornady cases in my 7mm RM come up with split necks after 1 or 2 reloads.