In the boot environment of the task, instead of choosing autoselect or the OS autoselect, you might need to specifically select the PXE boot image that you want it to use.  I've seen this happen before where it gets hung up as to which PXE boot it should really boot into.

What kind of HW do you see this problem on? It could happen in case you are trying to deploy the job to a server that has teamed NIC's and you are using the MAC address as the primary key. In this case you should add the serialnumber as a primary key too. the reason is that when you team two or more NICs they get a virtual MAC, which doesn't exist when you try to PXE boot.

But when you say that if you manually select the bootdisk into winpe, what do you mean? Do you mean that you manually select the WinPE at the PXE menu? In this case I suspect that the client will reboot to automation once WinPE is loaded is that correct?