I have run 6 builds to compile a huge kernel 6.8-rt8 with a full real time patch(s) applied along with the AUFS6.8 patches. All 6 builds finish successfully according to the log output. Configured with OverlayFS, AUFS and Btrfs built into the kernel on 3 runs and the other 3 only AUFS and Overlayfs are built in.
I used 4 different kernel-kits, 2 from @ozsouth and one Voidpup64 and a Ubuntu woof-CE ./merge2out assemblies
All six versions fail to boot going into kernel panic. First indications point to a problem with file system layering. Also the zdrv SFS and fdrv SFS seem to be incomplete or unusually small in size.