Also be sure to check by rebooting with both mouse buttons down that the partitions are visible in the early startup menu..
If not, then it can't be an automount bug either.
I remember having the same kind of problems with a 3.0 A4000 at some point in time, but I think those were solved by
- installing the correct filesystem in the RDB
- checking that the dostype of the partitions correspond to a findable filesystem
I was running PFS3 on the drive and it so happened that I had it in the RDB of my first drive, but not the second drive.. -> remove first drive, second one mysteriously broke
So also look to see that the dostype isn't plain vanilla FFS.