Updating plugins error messages for multiple plugins that error

[scole01]

When updating plugins and more than 1 plugin causes an error the first error displays ok, but subsequent errors don't show correctly. They show the first plugin's error message not their own.
When I update both plugins separately they both show the correct error message.
When I update both plugins together, the first is correct but the second shows the same error message as 1st even its name....

[scole01]

Image showing plugin update error messages

[Otto42]

Neither of these is in the WordPress.org directory, so presumably they have some kind of custom code to download updates from elsewhere.

Without knowing what that code is or how it works, there's no way to debug this and determine if it is a core issue or not.