Ok, I've seen the pictures, & I don't think I've ever seen a shell that badly warped. It's beyond use, & beyond repair. I'd need to see more pictures, especially side views with the drum assembled, & ultimately, see it in person to get close to a conclusion. I need more answers;
1/ how long have you had the drum? around 4 months
2/ were there any indications of tuning issues from new?the reso head was tight in the hoop, but other than that, no
3/ other than the usual procedure of tensioning the reso head, is there any chance you've tightened it down significantly on one side more than another? (let's say more than 1 - 1.5 full screw turns) only if the reso head had broken (had gone floppy, to try and pull a small amount of tension back)
4/ did you seat the head evenly before starting to tension it? yes, I'm pretty pedantic about tuning and seating
5/ did you inspect the shell for roundness from new? I did not. It was an off-the-shelf purchase that was a replacement drum. I took the shops word that it was good.
6/ when you finished a set by replacing the reso head with a tom head, did you crank that tom head very tightly to replicate a thinner reso head? No. As a rule I find a Tom head too thick to resonate properly, so I'd tune as low as possible to try and keep the snares moving
Here's my very initial thoughts. Causing this sort of damage by even the most uneven tensioning of a snare reso head is difficult to comprehend. Only if the head was placed on the drum, cranked down fully on one side, then tensioned to the max on the other side, can I imagine such a dramatic affect over a short period of time. A Hazy 300 or similar simply isn't capable of that sort of stress over a short period of time. Possibly progressive grossly uneven tensioning over a period of many weeks, + big atmospheric changes, may equate to such damage. I really need as much detail as possible re: timeline, etc.
My gut feeling (& this really has multiple caveats sprinkled all over it), is that the shell may have had a lesser fault from new. Progressively, you've tried to tune out the flat spot. This has subsequently placed a gradually more severe strain on the already weakened shell, & that's been compounded by further tuning adjustments.
Ply shells are inherently very strong, but even in ply, a 6mm un-reinforced (rering) shell isn't suitable for ultra high tensions. I can't see what lug type is being used, but I can see only two mounting points, one on each head end. As the shell weakens, tension on the single mounting point will further encourage the head to be pulled inwards.
Shells are strong because they're round. The moment they're not perfectly round, their strength diminishes hugely. Once they've reached that state, their ability to resist further forces is almost non existent. If a shell's already out of round, then even a moderate force applied unevenly over a long period can equate to serious warping of the shell.
The fact that the shell maintains it's warped shape when the heads are taken off, suggests a number of possibilities. 1/ shell manufacturing defect. 2/ severe variations in atmospheric conditions. 3/ gross & prolonged uneven tension.
Need more info.