We recently upgraded to D8 and I have been experiencing weird issues with Cron. Specifically, whenever the Cron is running, web pages are taking forever to load because cron is running some JS on the front end of any page you attempt to load. Specifically, it appears to be a timeout method that is holding up the page load.
NOTE: I will update this post and provide the exact JS file and function that is running on the front end the next time it happens to me. At the time of writing, cron wasn't running and therefore I couldn't inspect the web page to get the running method
I know it's not the CPU on the server because when cron was running it never got above 20% CPU utilization.
Isn't cron suppose to run in the background? Why would cron have a JS file being executed on every page, causing any page not to load until cron finishes?