Signed WebExtension listed as could not be verified for use in firefox

Add-ons Add-on Support
#1

I have a self-hosting non-AMO Firefox signed WebExtension that works on Windows 10, 7, Ubuntu, Mint, etc. Using Firefox version 56 and 57 (quantum). Works!

But in two machines says:
[extension name] could not be verified for use in Firefox and has been disabled.

One machine is Mint 18 on Firefox 56, and updated to 57 don’t solve the problem.
Another is windows… same problem.

Looking for this problem I found the signature sign and verify process
https://wiki.mozilla.org/Add-ons/Extension_Signing

The extension is signed WebExtension, not legacy.

Has this problem ever happened to you? How can I solve?
Does the message “could not be verified for use in Firefox and has been disabled” refer only to the signature verification process?
Is there any tool for debugging?

#2

That message refers to signing, yes. It’s possible that there’s something in those systems that is manipulating the XPI file or its contents. Antivirus tools can do this sometimes. Some things that you could check: 1) if the add-on XPI is installed as-is or is being unpacked into a directory, 2) if the hash of the file matches the hash on other systems where it works.