[User 224999]

- First of all I deleted the whole database, cleaned up cache, restarted Kodi and scraped again all my music. No benefits, everything like before (also because I did this after I upgraded to Jarvis).
- Then I tried playing around with skinhelper settings: disabling the online artwork search for music/pvr widgets immediately fixed the slow music widget. They are now instantly loaded like others when Kodi boots.
- There was still an issue: the Music random backgrounds didn't show up if not after an age or 2... Disabling the general online music artwork search (leaved on local one) fixed even this. After a first long loading, backgrounds are now loaded immediately on startup.

These issues are fixed in latest (beta) version of the skinhelper addon I posted yesterday.The widgets will now be fast even with scraping the artwork enabled.

So I guess that all my issues were because of the online script looking for every directory of my music folder for any kind of art, and of course being this made via ethernet slowed down the thing a lot.
But can you check if there is a way to speed up the scan for new items? I ask this because I see that while browsing albums, thumbnails or logos aren't loaded immediately like on video library, but they take a while every time. Does it scan everything every time? Is there a cache or missing list for this?

All info is saved in a cache. Once an item is scraped the info will be stored (permanantly) inside the cache. In your case it almost looks like the cache is malfunctioning which would also explain the slow loading times.
I am currently working on improving the whole music artwork scraping (as multiple users report it's not working optimal) so I need all the help I can get with testing :-)
Please give the latest skinhelper version 1.0.70 a try to see if that improves your situation. Also note that when you're inside the music library, in the context menu there's an option for "music artwork" (or artwork settings if you're on non-beta skin). Please open that and select the precache all artwork option. That will pre-scrape all artwork into the cache so it will be faster. Onc eit's in the cache it should load instantly.

Also I enabled the option to save contents under album's folder to make the work once of course, but I've seen that many times some logos/artwork aren't saved at all inside the folder. That's strange... and completely random it seems...

1. Enable the verbose logging for the skin helper addon (please do NOT enable kodi debug logging), you can ebale that inside the addon settings for skin helper service (also available with the music artwork contextmenu)

2. Navigate to an artist/album/song in your library and open the music artwork contextmenu again, press "refresh item (auto lookup)".

3. Repeat these steps for a few albums and check if the artwork is properly scraped.

4. Once you've done the above steps you can open your Kodi logfile in a texteditor and you can follow the exact steps the artwork scraper performed to get the artwork, check for any error messages, especially about the paths.

- The show right details view is still broken for "Big list 1" view (2 is working fine)

It's fine on my end. Are you on beta or stable of the skin ? Note that I didn't push a new stable version yet for a few weeks.

- The "supported addons" tab under quick skin settings is empty (the one from library views)

Thanks for the catch, will be fixed in next beta of the skin.

- Under settings> addons the "Downloading addons" section always shows squared view at first opening, no matter what view I choosed for that window. (already tried starting from fresh settings, it happens on all my devices)

Do you have forced views enabled for "files and main plugin listings" ?

- All views than "Titan Tiles" ones don't support touch/mouse as home/power buttons are missing. Can you enable them? I'd love to use the modern big horizontal list also on my Surface.

That's actually not true because ALL views support the touch buttons... except the new modern horizontal views.
I will add the touch buttons there too ;-)