Ubuntu 20.04.2 different versions of LXD

I have Ubuntu 20.04.2 on 6 servers. All apt-upgraded, but snap install lxd installs different versions of LXD: 4.06 on 3 of them and 4.15 on another 3.
Why? The OS is the same!
How to get the same version?
On servers with LXD 4.0.6 I try to update LXD snap, but got:

lxd version
snap refresh lxd
snap "lxd" has no updates available

How to upgrade 4.0.6 to 4.15?

Found the solution:
snap switch --channel latest/stable lxd && snap refresh lxd

Right, LXD comes preinstalled in a number of Ubuntu images.
When those are 20.04, the matching LXD LTS branch (4.0) will be used.

When you install LXD from scratch with snap install lxd, you instead get the latest channel which currently has LXD 4.15.

Running snap refresh lxd --channel=latest/stable will move any system currently on the 4.0 branch over to the latest branch.

Thank you.