If you stopped the engine while still on the slope the rear cylinder could have continued to have oil that was still in the intake drain into it, proabably enough to hyrolock...
I think the JK 3.6 gets away with it as it's lower compression. I'm thinking in the JL everytime it happens it's doing a little bit of damage to the rod, combined with the pinging in normal conditions it was only a matter of time...
UPD catch can. I wasn't running this setup until my new motor, the Teraflex kit out of the box doesn't mount into RHD. You can read the full report here
That's not a catch can it's just the check valve. It's a metal ball in a channel, when level ground it's open, when on an angle (noise up) it moves to block this path.
This is my RHD setup with the Teraflex kit. The circled part is the check valve. I do want to put a catch can inline to help with normal driving conditions unless the new PCV helps in those conditions.
The top of the bank holds way more oil than the catch can when on the angle, the catch can fills very quickly and becase it's at that angle as well it has reduced capacity too.
The current Teraflex setup stops the oil ingestion on the angles,but doesn't help with the excessive oil in normal...