V2V conversion; CentOS 6.9 from Xen to vSphere 6.5; VM won’t boot

I’ve been using vCenter Converter to migrate some VMs from a XenCenter 7.4 box to vSphere 6.5. Various Windows VMs have completed successfully but I’m stuck on the final CentOS 6.9 one. It’s transferred over OK but when I boot it, it gets past the Grub loader then stops on a black screen and a non-blinking underscore cursor.

The disks have come across as SCSI rather than IDE (good I think?) but I’m at a loss as to what to do next. Could it be an issue with a non-Spectre compliant Linux kernel attempting to run on a patched ESX host?

thanks

Calum