Install failed, stuck with /?doing_wp_cron=

Hello,
I downloaded the plugin and tried to upload it. I ended up on a 404 page.
Cloudflare stopped redirecting to my site because it was too slow to respond. (522 error)

I managed to get my site back online.
But I am stuck with ?doing_wp_cron=1464077598.6235411167144775390625
Always being added to the end of my URL.

I don’t want to disable cron because I have plugins enabled that need it.

How do I stop it from being added to my URL
Is it still slowing down my site?

What is going on?

https://wordpress.org/plugins/all-in-one-event-calendar/