Can't connect Jetpack or IFTTT to Wordpress on Ubuntu 16.04 LAMP

Dear community,

I’ve migrated my Multisite Network from an Nginx server to a LAMP Stack (PHP7) with Ubuntu 16.04, via the export/import function. I’ve managed to fix most issues, but I’m still having issues with Jetpack integration and connecting to IFTTT.

Info and debug logs Jetpack debug:

site_inaccessible Foutdetails: The Jetpack server was unable to communicate with your site [HTTP 500]. Ask your web host if they allow connections from WordPress.com. If you need further assistance, contact Jetpack Support: http://jetpack.com/support/

SELF:
	Array
(
    [headers] => Array
        (
            [server] => nginx
            [date] => Tue, 31 May 2016 18:33:21 GMT
            [content-type] => text/plain;charset=utf-8
            [connection] => close
            [expires] => Wed, 11 Jan 1984 05:00:00 GMT
            [cache-control] => no-cache, must-revalidate, max-age=60
            [pragma] => no-cache
            [x-hacker] => Jetpack Test
            [x-ac] => 3.ams _dfw
            [strict-transport-security] => max-age=15552000
        )

    [body] => {"error":"Can not resolve domain nameservers","error_description":"We were unable to resolve the nameservers for your domain. It is likely that you have recently registered your domain name. It takes several hours for new or transferred domain names to start working, so please come check back later."}
    [response] => Array
        (
            [code] => 400
            [message] => Bad Request
        )

    [cookies] => Array
        (
        )

    [filename] => 
)```

As you can see, this debug logs says Nginx, while my sites are all running on Apache now. I've deleted Jetpack, re-installed, but to no avail. 

A similar issue occurs when I'm trying to connect any website in my network to an IFTTT service. "Live channel fields value is not a valid Wordpress url"

**What I've tried**
Server reboots
Disabling all plugins and themes
Re-installing Jetpack

I've done some research and people with similar issues seem to have an issue with their XML-RPC Server .php file. I have this .php file on my websites and it seems to run normally: server accepts POST requests only.

I haven't set up a firewall, so that shouldn't be an issue. 

Is there anyone that might have an idea on how to resolve these issues? I assume they're linked. 

Thanks in advance. :)

Kind Regards,