Comment 8 for bug 1915579

That file mode must have been lost during the last merge...
I've prepared a fix for the 664 -> 755 mode change of /usr/share/initramfs-tools/hooks/lvm2 available in this PPA (currently building):

https://launchpad.net/~slyon/+archive/ubuntu/lp1915579

Could you please check and confirm if this is fixing the problem for you?