You may want to offer the database to support or try MediaMonkey 5 to have it rebuild (better than complete optimization in MM4) the database as it's likely a database corruption.

OK. So I tried out what you suggested by changing the Album Artist for the four albums to the original "Herrmann, Bernard" (1 space). So this Album Artist is no longer appearing under Album Artist node. Going to location and going to a track in the first album choosing Same as Album Artist found nothing.
Having then changed back to "Herrmann, Bernard" (2 spaces) and repeating the above switched immediately to the Album Artist entry showing the four albums.
Really what I was expecting in that the original Album Artist just won't appear.

It would be interesting to see what MediaMonkey does as it may provide a clue. Find More from Same is part of the right click Context Menu on files.

No. I'm not sure where this can be found.
In any case I think that is possibly irrelevant as I can see the missing albums listed under the top level of Album Artists, even though the Album Artist itself isn't listed as a folder. So these albums are recognised by MM

Did you try Find More from Same > Album Artist?

Thank you Lowlander for your reply. I ran Maintain Library with complete optimization - it made no difference. It ended without any information or message. I'm not sure that optimization is going to correct errors - sound more of a performance thing. Some sort of validation function is really what is needed.

It is only Album Artist that I have this problem with. The 4 albums I have now with Album Artist "Herrmann, Bernard" (2 spaces) didn't have any tracks with him as Artist. I temporarily changed the Artist for one album to be "Herrmann, Bernard (1 space) - this works fine as this artist name now appears under Artists as expected. Also all 4 albums appear under Composer node "Herrmann, Bernard" (1 space) as they always have.

Following the Maintain Library I tried again - I changed Album Artist on 1 of the 4 albums from "Herrmann, Bernard" (2 spaces) to "Herrmann, Bernard" (1 space) and the tracks disappeared leaving an empty album, as normally happens, but no corresponding "Herrmann, Bernard" (1 space) entry appeared under Album Artist.

So the problem still exists. It's seems that Album Artist "Herrmann, Bernard" (1 space) has become hidden somehow within the Artist album list but everywhere else it is ok!

I would have thought that a database integrity error would display an error message (or crash).

Be careful with the different between Artist and Album Artist. You could try using (in the Location node where you did find the files) right click > Find More from Same > Album Artist value to see if you can locate them that way (if it's a user error).

Or run File > Maintain Library with complete optimization checked (fix a database error).

You can also use Artist & Album Artist (may need to enable under File > Manage Collections) instead of Album Artist to see if files are found under the correct artist value that way.

This is really odd. I discovered this a few days ago running 4.1.25 (I think) and having updated to 4.1.31 have the same problem.

I have four albums with Album Artist "Herrmann, Bernard" except that they were no longer appearing in the Album Artist List. "Herrmann, Bernard" doesn't appear as an Album Artist in the list. The albums do appear at the top level of Album List

Going into Location I can change the Album Artist via Properties for each album to something else, e.g. "Herrman, Bernard" (dropping an "n"), or placing an extra space between the comma and Bernard and the albums then appear correctly under that new name in the Album Artist list.

If I then try to put the name back to what it should be, i.e. "Herrmann, Bernard" the album artist again disappears from the list.

I have found this on another Album Artist "Barry, John" with 15 albums - in this case "Barry, John" does appear under Album Artist but only 2 of the 15 albums are shown. Nothing I do will make the other albums appear with the two that are listed correctly (again they are shown correctly under location). Additionally in this case where several of these albums have Genre of Soundtrack, only one appears in the Genre/Soundtrack/"Barry, John" list and that one is NOT one of the two appearing under Album List! They do all appear at the higher level of Genre/Soundtrack.

So for the time being I can get missing albums to re-appear by modifying the Album Artist to be mis-spelt or by adding extra spaces but that is not ideal. I tried re-scanning a couple of albums from their location but that makes no difference.

It seems to me there must be some sort of relationship errors in my MM database. Are there any scripts that can be run to identify and correct these issues. Or some way to create a new version of my database without these issues (short of reloading all the CDs!)?