Hi
I have got this to work – eventually after days of head butting the wall!!!
Here’s how I’ve set it up.
Only tick “Overwrite Default Categories” in the first instance of your Category widgets, DO NOT select it in any other of the multiple Category widgets you’ve used afterwards.
DO NOT select either “Allow users to select more than one category” nor “Display categories in hierarchical mode” in any widget.
ONLY use the “include” option to list the categories you need to be able to select within the widget, DO NOT not use the “exclude” option at all, it seems to confuse the plugin if you try and use both options.
(The little plugin “Reveal ID’s” lets you see your category ID’s
https://www.schloebe.de/wordpress/reveal-ids-for-wp-admin-25-plugin/#english)
I’ve then used the drop down menu method for selection in each of the 3 category widgets which seems to work, I couldn’t get the ‘List’ option to work – no idea why!
Hope this helps everyone!