Comment 68 for bug 1652270

This is related to bug #1652504 and the answer #16 there is a more detailed explanation of #65 above:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1652504/comments/16

As of 18.04.2 the fdt_addr has changed again, I was able to fix this via the following, first cat boot.scr on the primary partition, there's a bunch of binary at the start of the file followed by fdt_addr_r 0x03000000 - this is the new device tree address.

Use that as the base value on config.txt:

device_tree_address=0x03000000

You do not need to set device_tree_end, this got the pi booting again.