Problem with 504 error timeout

I am having issues with 504 errors on my website. I contacted my host and they deactivated all my plugins (which stopped the problem). I started with reactivating WPMU dashboard then defender then the issue started happening again so it's likely the cause. I want to know what can be done since I can't have my site constantly getting errors but I'd really like to be able to reactivate all my plugins from WPMU to protect and backup my site.