OpenVPN iOS cliënt app very slow

Hi all,
My MacBook has a decent OpenVPN connection speed to my netgate firewall, even when on the road when the MacBook is tethered to my iPhone.
But when I connect that same iPhone to the same OpenVPN server I get 2-4kB/s, slow enough to load my pfSense dash in two minutes.
I simply went to pfSense-> OpenVPN cliënt export utility and created an iOS package, which was instantly recognised by the OpenVPN iPhone app.
Any suggestions what could have gone wrong here?