Defender and error 500

Hi,

after installing defender on my multisite installation bizinthe.cloud I am redireted to an error 500 page after every login. https://goo.gl/bNYq2z I seem to be logged in because I can open /wp-admin and work from there.
I already talked to support about this. They said it is an problem with my host (cloudaways). My host tells me to deactivate the plugin because its not working...
So what can I do?

regards

Heiko