Also seeing similar problems… We have been using images: with LXD (LTS and non-LTS) until now. Was working on some infrastructure changes for our LXD-based CI runners and discovered this weirdness with LTS-based LXD and “normal” LXD seeing a different set of images… until I found this thread half an hour ago. 
My problem is that LXD LTS does not work for our use case, because we use functionality which got released as part of LXD 5.1 (LXD 5.1 has been released), specifically the lxd image copy --profile flag…
So I’m currently stuck with an LXD LTS which doesn’t work (because we can’t differentiate the profile being used on Ubuntu and Rocky Linux-based guests, which is needed for proper operation) but can access the images, or an LXD non-LTS which works but can’t access the required images. 
Or, we can switch to Incus which is not released as a stable version yet. I’m not sure I’m willing to put this on our CI infrastructure just yet.
Sorry of this sounds very negative, I’m just frustrated after wasting some time on this today. I know this is not the fault of LinuxContainers.org. It’s just so incredibly sad to see all the extra work and pain this incurs on a lot of people in the community. 