I have just reinstalled and dragged it to the programs folder. After running an import of the library from the nas server - the program stops suddenly with a fault message.
I'm going to make a guess here: You might have one or more "bad" media files that MC is trying to import. Turn off auto import for now and see if it stabilizes. If it does, you can turn on logging, then make it crash again, and send in the log (here in the forum). Then someone can probably tell you why it's crashing. Hopefully they'll find the file or files that are making it crash.
To disable auto import: Tools > Options > Library & Folders > run auto import in background > (uncheck)
If I look at the tagging value in j river the field is empty - if i look at the same value in metadatics it is not empty but filled out with the correct disc number.
As it works fine in other programs I think this must be a fault in JRiver for Mac.
Hmm. I'm certain that MC recognizes the tag named [Disc #] because I RIP CDs with an external program that adds this tag and MC reads it every time. I wonder if Metadatics is adding a different field name with the disc number?
I just downloaded Metadatics and opened several FLAC files on my system that are from properly tagged multi-disc sets. I read some files that have disc numbers and Metadatics showed them. Then I removed the disc number from one file with MC, and loaded it into Metadatics. Metadatics did NOT see a disc number, so I added it in Metadatics and saved it. MC saw the change in disc number after Metadatics saved it.
I conclude that Metadatics and MC definitely work correctly together with Disc number. Load up some of your problem files into Metadatics and see what it shows for disc number. I'm betting Metadatics will NOT show a disc number at all.
The other programs, that seem to be sorting correctly, are probably sorting based on the file name, which *probably* has the disc number in the file name, or in the directory name. If that's the case, we can add disc numbers for you based on those names, either with Metadatics, or with MC's "fill properties from filename" feature.
Let us know what you come up with. ...and good luck!
Brian.