I might have noticed it before with a different theme, but I was looking at what Morkkos I had and the pet codex said I had 8 Themed Florid Fungus Morkkos. I didn't think I had that many, so I checked with Advanced Search, which pulled up that I had 3. I thought maybe I had done something to make the numbers weird in Advanced Search, so I refreshed it and input again for pets belonging to me that were Florid Fungus Morkko. This again only pulled up three. Thinking it was probably still user error, I went through my stables and checked for all Morkko just to be sure, and again only came up with three. I feel like I have had this issue before, but dismissed it as me just being stupid, but now I think this might actually be a bug.

Is anyone else experiencing a problem like this?

I'm pretty sure the advanced search may be counting past pets you had as well? Like if you sold them off or released them? Maybe just releasing them, because I know I currently do not have any Beautiful Evening Luporas, but I did at one point and released them. Yet it still tells me I owned 1 themed and 9 purebred of them. I also know I released two Persephone's Familiar Morkkos, though it tells me I own 2. So I think if you owned it at some point it still counts? Still wrong, but I think that's where your 8 is coming from

Yup, I'm having the exact same thing happen for me, but only for pets I've released, not ones I've sold.

It includes any in your possession, which includes currently released pets. Using the search, it shows that you have a total of 8 Florid Fungus Morkko, 5 of which are released.

I see, thank you all! It really was just user error, haha!