Questions about quality scans

I am at the moment a little bit confused.
I have 2 Bluray-Scanner accessable to run scans.

For some media the results are pretty similar, for some other I get huge differences. How to interpret this?
Are the results of the PX-B310U reliable at all?
I know it is only a Blu-Ray-Reader.

Scans of Disc 1:

And Disc 2:

Or what could be the reason?
Scans of a third disc:

Last disc rescanned after opening and closing the tray - now I get again the expected results :confused:

What does this mean? I am clueless. I cannot scan every disc twice.
Did you ever had similar experiences with one of your drives?

But the results of the disc with the TDKBLDRBD MID I could not improve by reinserting the disc.

I believe that a few of us have run into the same odd behaviors when trying to scan with BD-ROM drives. Whether this is a result of the hardware not being up to the task or ODC not handling them well, I do not know.