After extended tests (see posts below for details) I can be more specific with my warning: Without having experience with Picard under Windows, it seems that both the “stable” version 1.4.2 and the (beta) 2.0.0 dev6 have serious stability problems under the actual macOS, which even can render the Picard installation unrecoverably corrupt, i.e. which can not be corrected even through a complete dis-installation and clean new installation. When my original post stated “My problem is solved”, then I had been in error.
The final unrecoverable corruption may be correlated to having both 1.4.2 and 2.0.0 on one system, or to having installed plugins which do something bad “behind” in the system… I simply don’t know despite my extended tests.
Through very special luck I was able to revert to a complete system backup, which still had Picard in such a state, so that from this state I could repeatedly do tests about possible ways, how to get to a stable Picard system.
For me this ended up with a sole 2.0.0 dev6 installation, with an updated fpcalc version 1.4.3 for good retrieval performance. With this I am happy again, because I’m anyway doing only manual maintenance of my iTunes mediathek (according to some, the Picard<->iTunes integration anyhow shall be not the best…).
So if anyone comes “fresh” to Picard and/or has not yet ran into problems, I recommend just doing solely this 2.0.0 installation (I find 2.0.0 a tiny tad easier to use than 1.4.2, and with slightly better retrieval performance).
========= Original initial Post: =========
My problem is solved, but maybe my experience can help others. But this needs some explanation of my background:
I’m a Picard newbie/layman currently overhauling a small 4’000 song iTunes mediathek on the latest macOS 10.13.6. I do this album per album, and a week ago I stumbled upon MusicBrainz Picard. WOW! What a great instrument. I do not need automatic iTunes updates, but just to find the information which I then can manually input into the iTunes mediathek, using their “title information” interfaces. Because I liked Picard so much, I also tried the newest 2.0.0 Dev 6, which I found even a small tad better. I stopped my experimental uses of Jaykoz and Yate, because - honestly - I even did not understand how to operate them.
But then - just for curiosity - I installed in Picard 1.4.2 the “Classical Extras version 0.9” plugin. But because I didn’t really understand how to operate this, I simply ignored it.
But somewhat later both Picard versions (1.4.2 and 2.0) appeared to work much worse. I did an uninstallation for both, tried to find implicit system files and purged them as well. Then I did new “clean” installs of both Picards. But now 1.4.2 took a real eternity using “Scan” for “loading album information” in the right half of the UI. Sometimes it took 15 minutes, sometimes it didn’t end successful at all.
Picard 2.0 even didn’t start any longer at all. When I manually started its “Contents/MacOS/picard”, then I got some strange messages in the system terminal…
To cut a long story short: For 2 full days (!) I tried everything again and again, but without any success. Only after finding the related plugin library with Finder and deleting it, I could do a successful reinstallation of both Picard versions. And suddenly everything now ran fine again, like in the beginning. Strange, but true…
Hope this helps any poor soul having run into the same problem…