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The fact so many people are having this issue across various systems, together with everyone's plugin update working before the upgrade, then maybe this is omission of WP failing to remvoe relevant directories before updating.
1 experiencing the same issue Please let me know if you would like any further information, or testing.
(Cannot create directory as it already exists) I have to think this is an issue with how the update in WP 4.4 via ftp is completing the updates.
It is obviously failing to remove the directory (Even with full permissions granted to everyone and trying all users and groups) If one can roll back a version and the updates work but then move to the latest WP and they do not (Leaving all permissions the same) would this not be an issue with 4.4 not removing existing directory and files during the update.
It seems that, for some reason, the formatting of the Package installation failed: There was an error installing the requested package.