Same problem, here, with adding songs to My Music: Sometimes it works; sometimes it doesn't.
To those with this issue:
1. Are you an iTunes Match subscriber?
2. If so, are you over the 25,000-song limit?
I am both, and it seems that may be related to the "Add to My Music" failures. Having exceeded the limit, I'm fully aware that any songs/albums that I add to iTunes will no longer be uploaded/matched. (Apple is working on increasing the limit to 100,00 songs.)
But having subscribed to Apple Music, which is a separate product, I should be able to freely listen to anything in Apple's library (which is indeed the case), and I should be able to freely add songs to My Music (which sometimes works and sometimes doesn't).
Observations:
- On the Mac (El Capitan beta + iTunes 12.2.1), I cannot add songs to My Music at all.
- On an iOS device, adding to My Music works about 1/2 to 2/3 of the time.
(If I try it on iOS just after attempting to do so on the Mac, the iOS device fails every time. Not sure if that's absolute or anecdotal, but it's happen 3 times. Then, a day or so later, adding to My Music works again on the iOS device.)
I'm sure Apple will resolve these issues in time; it was a massive roll-out. But it's frustrating that we who've been paying for iTunes Match all along are now essentially being "penalized" for that, as it seems (based upon what I've read in various forums) that non-iTunes-Match customers are experiencing fewer problems.
The problem is that my 90-day Apple-Music trial is ticking away, despite my not being able to fully experience it by adding (consistently) to My Music. So, I called Apple support and explained this to a rep, who agreed to reset my Apple-Music trial in the future, once this issue with My Music has been resolved. That way I'll get to properly "test-drive" the service, as intended.