Some paths in SFZ files are in all lower cases while the real path contains capital letters. To reproduce, try loading Brass - Bass Trombone Solo KS.sfz in Carla 2.2.0 on Linux.

as per #1 , sampling+ is a bad license choice , but perhaps even more importantly there is no easy way to use it . there is no single complete list of contributors that needed to be attributed per license requirement in every song that uses these samples ; failing to do so exposes one to law-suites (however good-willed original authors of samples were , their heirs might be a different story and with current fucked up copyright laws you'll only get in the clear 70+ years later) at any moment . furthermore , any changes made after initial release by original author violate sampling+ license , and by proxy would any composition using them (even if some form of attribution given is deemed acceptable) . i'm not a lawyer , so i'm not sure if these violations can be prosecuted without authors' consent , but again , their "intellectual property" heirs may decide it's worth extorting billions dollars from free culture enthusiasts

Currently, the license conditions cannot be met, which means those with power of attorney can sue anyone who uses the samples. This has been explained in two other issues: #4 and #1.

The problem

The license (https://creativecommons.org/licenses/sampling+/1.0/legalcode.en) has conditions that can't be reasonably met, and which pose a massive legal risk to those who use the work. Here are the main reasons.

Prohibition on advertising

All advertising and promotional uses are excluded from the above rights, except for advertisement and promotion of the Derivative Work(s) that You are creating from the Work and Yourself as the author thereof.

If you use SSO to make some music, and you put that on your bandcamp, and you have other music on your profile that doesn't use SSO, you are advertising it with SSO derivative works and are in breach of the license. If you use SSO to make some music, and then you post that on your youtube channel, and you have other random videos on your channel, you are in breach. If you play music created with SSO while streaming on twitch or making a video on youtube or doing a podcast, with a banner or a product review or a paid promotion, you are in breach. Any use of music made with SSO that isn't on a blank webpage with no links and no information given about the artist, could be considered a breach. It all depends on what a judge defines "advertising" as.

Attribution and Notice

If You distribute, publicly display, publicly perform, or publicly digitally perform the Work or any Derivative 
Works or Collective Works, You must keep intact all copyright notices for the Work and give the Original 
Author credit reasonable to the medium or means You are utilizing by conveying the name (or pseudonym 
if applicable) of the Original Author if supplied; the title of the Work if supplied; to the extent reasonably 
practicable, provide the Uniform Resource Identifier, if any, that Licensor specifies to be associated with the 
Work or a Derivative Work, unless such Uniform Resource Identifier does not refer to the copyright notice 
or licensing information for the Work; and in the case of a Derivative Work, provide a credit identifying the 
use of the Work in the Derivative Work (e.g., "Remix of the Work by Original Author," or "Inclusion of a 
portion of the Work by Original Author in collage"). Such credit may be implemented in any reasonable 
manner; provided, however, that in the case of a Derivative Work or Collective Work, at a minimum such 
credit will appear where any other comparable authorship credit appears and in a manner at least as 
prominent as such other comparable authorship credit. 

"Derivative Works" and "Work" are mixed all together in this, so it's vague as to what you need to do, but here we go.

You must keep intact all notices that refer to this License and to the disclaimer of warranties

This means a license.txt must go with the music, but that means if it gets separated you could still be in hot water. Then there's metadata, but that's not "keeping intact all notices" now is it.

The rest is basically indecipherable because it's just a giant list of conditions mixed with alternatives, so you'll need to read it all. The gist though is you need to display (any, in order of priority)

Name or pseudonym of SSO (including later contributors..?), title of the Work

and

Uniform Resource Identifier (NOT defined anywhere in the license, we have to assume URL)

Such credit may be implemented in any reasonable manner

There is no reasonable manner, this license is broken. Does this mean putting the credit on your music page but NOT in the music meta / folder is acceptable?

What to do then?

I suggest, that until someone finds out exactly where all the samples came from and recreate the SFZs under a permissive and not broken license, a warning is added to the readme to warn people of the license issues. These are not paranoid speculation, but represent real potential future legal threats to the users of the samples. You can argue all you like that "the people behind it are in good faith and won't sue you" sure, but that doesn't mean you're not vulnerable, with a threat hanging over your music forever. You can still be extorted for example if the power of attorney is passed to an heir or other party, and they notice you're making lots of money off your music or something. A possible warning could be:

Warning regarding copyright

The license in this project has been retired by Creative Commons, and poses some legal problems to people using the samples and plugins. Even though litigation over this is astronomically unlikely due to the good faith of the creators of the work, caution should be taken and the license should be read and understood before making a decision to distribute music made using the works.

The cutoff value for the high-pass filter on the Celli sustained instrument is wrong. This causes no audio to render. Removing the filter entirely works, but I'm not sure what value you were actually going for. Also seems to be wrong on the KS version.

SSO currently uses proprietary license called CC-Sampling-Plus. Since Matthias no longer maintains SSO, maybe he can change the license to something free such as CC-BY or CC-BY-SA?

Also, the sources of the files are not clear and if some original files are CC-BY-SA (which falls under "CC-licensed") then Matthias doesn't have permission to relicense them as CC-Sampling-Plus.