Problem still persists on newer firmware. The support advice for the problems I face with block size is to perform Long Erase on all medium and go from there as in nearly all case this fixes that issue.
For anyone else here is the error message I got.
Failed to prepare to start new tape session: StartSessionTape failed
When accessing a new tape of a multivolume partition, the current block size is incorrect.
Tape read error
Apparently there is changed logic in v8. Now block size is considered in order to have less issues with restore from tapes.
So at 3hrs per LTO-5 tape it is a long process. At least I got 4 drives and only 80 tapes to operate on over time as they expire.