I can see that my colleague from the support team has handled you there 
I also informed him internally what I noticed/found on your Staging site, and most likely the Fatal Error was due to the incorrect email set in the wp_options ( admin_email ) - which somehow got changed during the search and replace process (and the email address would look something like this incorrect email format: info@https://yourstagingsitename.kinsta.cloud ) .
This is a known bug issue with DevKinsta indeed (similar to what has been reported in the other thread here as well) and we have reported this issue before to our internal devs team 
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So yeah my colleague will help to assist you on how to change that email address with the correct mail address/format. I told him the same about this and the solution that can be tried (as shown here as well)
Regards,
Agus