May be I add my solution here: The errors are caused by Apple fork files. They are created when transferring or even copying files by Finder, and FileZilla and also Cyberduck, though stated otherwise for Cyberduck as I understand, don't ignore these system files during upload.
You can look for these files beginning with ._* in Cyberduck or FiliZilla and delete them - There's always a corresponding file without the .- before. Be careful not to delete .htaccess and maybe other needed files.
You have to turm on "display hidden files" in FileZilla and Cyberduck to see the ._ * files.
It doesn't depend on which MODx Version or which download file, as sometimes supposed, as long as the download files are not corrupted. The error also occors with other CMS systems.
Cyberduck help says it ignores these .-* files and dosn't upload, but that didn't proove true for me (Version 4.2.1)
There is one more tip: remove the Apple quarantine bit from the files by shell, using
find . -exec xattr -d com.apple.quarantine {} \;
I didn't try that.
Removing the .-* files from manager directories (esp. the includes/lang in my case) helped me.
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