Defender plugin stopped scanning at 57% and will not cancel

My Defender Scan is stuck on 57%. It won't complete or close. It is slowing the site down considerably.

I cannot deactivate it.

This is a development site for Finfashionplus.co.uk where it also happened. The only way I could stop it was to FTP in and delete the plugin. When I reinstalled it it shows that it is still scanning and on 57%.

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