da0s1 is just the MBR name for the first slice. It's not pre-GEOM at all, and GEOM redid the 'slice' code we had before, but kept the names.
Usually this means either (a) the volume was uncleanly mounted and the mount code in the kernel is detecting that and rejecting it. This would be true of UFS, but that's unlikely on an MBR device. FAT/MSDOS filesystem wouldn't have this problem. or (b) the code that mounts it is missing or was damaged in the update process. pkg + kernel modules are known to not get along, so it's possible that if you were using FUSE to access the device, the new fuse binaries don't work with your kernel.