PXE Boot not working until hard shutdown

We have a lot of servers that boot over the network via ipxe. Some of the vms (all affected are on random hypervisors) fail to boot over the network after clean reboot from inside the vm. To get them to boot we have to hard shutdown them from ON and then after powering them on, they would boot as expected.

Versions of the related components and OS (frontend, hypervisors, VMs):

ON - 5.4.0
Hypervisors: Centos 7, llibvirt 3.9.0
Vms - not installed on disk so irrelevant

Has anybody experienced something similar? Any idea on where to look what might be happening?

Thanks in advance