Comment 66 for bug 1768230

tl;dr: initramfs-tools 0.130ubuntu3.5 and running update-initramfs -u seems to have fixed it.

I have been putting up with this problem for months, thinking it was due to a kernel update (from 4.13 to 4.15). Finally, I find this thread today. Anyhow, here's my info:

OS: Linux Mint 19 (based on Ubuntu 18.04)
Kernel: 4.18.15-041815-generic kernel
initramfs-tools version: 0.130ubuntu3.5
LVM root and swap partitions setup during install
Symptom: waiting 30 sec during boot, with message "failed to connect to lvmetad" ....... "falling back".

After reading previous comments, I did following:
sudo vim /etc/initramfs-tools/conf.d/resume
 .. changed from RESUME=UUID=e6675202-6e2f-4c1b-b6e6-4ffe3ef7c882
 .. to RESUME=/dev/mint-vg/swap_1
sudo update-initramfs -u
  ,, (this indicated that it would only apply to latest kernel, not older ones, which is what I wanted in case it borked my boot)
reboot

It now boots without the 30sec delay, but does display a message about "[something something] disabled by BIOS" or somesuch. This seems to override the mint logo that would normally display during boot if one did not press del to see boot messages.
Note that I only guessed that RESUME=/dev/mint-vg/swap_1 would work, since I do want to be able to resume from sleep, but not sure if that's the correct syntax for the resume file, but it is a valid symlink for my swap partition, the alternatives being /dev/dm-1 and /dev/mapper/mint--vg-swap_1. Resume from sleep still works, not sure if it'd affected by this anyhow.

Finally, I apologise if reporting on mint 19 is not welcome/appropriate here, but it is based on ubuntu 18.04 and I did have relevant info to contribute.