iTunes Match and iCloud Music Fail

I've been experiencing a frustrating problem with Apple Music on my Mac. Context before the problem: I have a 700GB library of music on an external SSD, I have rolled through multiple Macs and hard drives over the years, but maintained my metadata for this library since 2006.

Problem 1:

In my current arrangement, whenever I try to 'consolidate library' I get an error (-54). I have tried troubleshooting this multiple times (trying to find locked files, tried a different external drive) and not had any success.

Problem 2:

For files that were part of an initial iTunes Match upload years ago, I now encounter some will play, some will play only for a few seconds and stop, and some won't play at all (I force skip). I posted about this earlier this year here. I attempted many of the troubleshooting suggestions to no success, then thought I had discovered a solution whereby I download the file from my iCloud/iTunes Match and then delete whatever duplicate was in my drive's folder. This works about 50% of the time, but the other times it causes the app to crash and requires a full reboot of my Mac.

Solutions I'm seeking:

-How can I retain my library metadata while pointing it at the 700GB music files such that it recognizes the album/artist/song, etc.? Consolidate library is the only way I know to do this, but I can't due to the error.

-How can I get past this iTunes Match/iCloud library bug with my matched files? I wonder if canceling iTunes Match would solve for this since I pay for Apple Music streaming? I read in another post that iTunes Match is really only useful to match files that aren't in Apple Music, but now iCloud library does that anyway. Is there another way of 'rematching' files?

Appreciate any help on this.