I had a look at that syste using ipmi.
And it looks like a proxy was added to the petitboot ('BIOS') and I assume PXE through proxy didn't work well.
Hence I removed the proxy conf from petitboot (and also added boot from disk as 3rd boot option - which was missing) and kicked-off a deployment of 18.04 and it worked for me again ...
An open question is still that MAAS didn't timed out and stayed in status PXE boot for more than a day?
I had a look at that syste using ipmi.
And it looks like a proxy was added to the petitboot ('BIOS') and I assume PXE through proxy didn't work well.
Hence I removed the proxy conf from petitboot (and also added boot from disk as 3rd boot option - which was missing) and kicked-off a deployment of 18.04 and it worked for me again ...
An open question is still that MAAS didn't timed out and stayed in status PXE boot for more than a day?