Using OVMF version 2.6 this works fine, but using  OVMF 2.7 the guest no longer boots from the USB device.

Option 1) For it to work I have to set the boot order on the USB device and once the OVMF Shell appears I can reset it and it will find the USB device and boot.

Option 2) Another setup which works if I remove all boot order settings from the guest and have a boot dev = 'fd' and this works every time.but I cannot add multiple entries.

  <os>

    <type arch='x86_64' machine='pc-q35-5.1'>hvm</type>
    <loader readonly='yes' type='pflash'>/usr/share/qemu/ovmf-x64/OVMF_CODE-pure-efi-tpm.fd</loader>
    <nvram>/etc/libvirt/qemu/nvram/b96bfc99-3612-0daa-9d8c-69e9d550d05a_VARS-pure-efi-tpm.fd</nvram>
    <boot dev='fd'/>
    <boot dev='hd'/>

Any thoughts on how to get option 1) to working without having to do a reset.