Resizing generic-ext4-combined-efi

[Torbjörn Jansson]

Hello all.

i'm trying to install a fresh copy of openwrt 21.02 using this image:
openwrt-21.02.0-x86-64-generic-ext4-combined-efi

i can get it to boot and so on, but my problems start when i want to expand the 
image to get more space.
resizing the disk works fine.
running gdisk on it to just fix the secondary gpt header also works and it 
boots fine.

BUT as soon as i change the size of partition number 2 (the largest one) so it 
covers the rest of the disk it gets stuck during boot.
i have expanded many partitions before by removing partition, then carefully 
creating a new one with same start sector and a new end much further up on the 
disk then later running for example resize2fs on it.

But this time it gets stuck at boot with "Waiting for root device 
PARTUUID=random numbers"

How do you expand the filesystem on ext4-combined-efi image?