Defender breaks site when activated but won't allow plugin deletion

I'm not sure what's going on, but I was just trying to do some basic security clean-up with Defender when my site went completely down. I had run a scan and then also was trying to let Hardener "prevent php execution," but my site went down when I allowed it to create/edit .htaccess files. I'm not sure if this is because the scan hung or because of the .htaccess files -- I think what happened was I clicked on the Hardener notice in my WPMUdev Dashboard while the scan was running simultaneously on the site, which in retrospect was probably a bad idea. I had to contact my hosting service to restore my site, and they deactivated the plugin on their end, which got me back online.

When I tried reactivating Defender to edit settings and try to get it working again, my site immediately went down again and my host had to deactivate Defender again. I decided I should just delete the plugin so I don't inadvertently break my site again, but I get an error when I try to delete it:

Fatal error: Cannot use object of type WP_Error as array in /my_directory/wp-content/plugins/wp-defender/app/module/scan-module/model/class-wd-scan-result-core-item-model.php on line 275

I had been using Defender just fine previously, although I did recently change hosts (from DreamHost to SiteGround -- I am VERY happy with this switch overall). I asked my host if they just weren't compatible with Defender, and their support said:

It does appear that it most probably is not compatible with the current version of WordPress as using it is causing some WordPress core files to go haywire. I recommend considering utilizing an alternative for this plugin or double-check with the developers for it's compatibility with WordPress 4.5.

Is this indeed a 4.5 compatibility issue, or a hosting issue, or did I just find some weird bug, or...?