Plugin download problem

Hi
I’m using version 2.575 on RPi3B.
I have successfully installed plugins (as part of UI setup) in the past - but they are no longer downloading and these are the details:

Downloading plugin at volumio.github.io/volumio-plugin … ontrol.zip
END DOWNLOAD: volumio.github.io/volumio-plugin … ontrol.zip
Creating folder on disk
Unpacking plugin
The following error occurred when installing the plugin: TypeError: Cannot read property ‘name’ of undefined

The thing is, I’m not doing anything different. All I do is click ‘install’ - same as I always did.
When other people have reported this installing error, I think they’ve been told they need to download the unzipped file.
Like I say, I only click ‘install’, I’m not telling it where to look so I don’t know what file it’s finding - and I wouldn’t know how to install any file I find as a plugin!
I would be most grateful for any advice on this problem.
Thanks.
Graham