Well, the red instead of white does sound like a glitch in the default resource pack with the collar texture. You can test this by using a dye on the cat and seeing if it changes color. The "moving while sitting" part also sounds like a resource pack glitch, the animations seem a bit broken too. If you have any resource packs turned on other than the default one, turn them all off; if you have none turned on, turn one on and then off again. After doing one of these things, see if the problem persists.
Your other cats disappearing is a glitch that happens sometimes. Just close the world and open it again, and if the other cats still aren't there, keep trying until it works. If it still refuses to work, I don't know.
As for the "demon" cat not eating any fish, I'm not sure what would cause that. Maybe a behavior pack glitch, similar to the resources glitching?
Team4tress237
Well, the red instead of white does sound like a glitch in the default resource pack with the collar texture. You can test this by using a dye on the cat and seeing if it changes color. The "moving while sitting" part also sounds like a resource pack glitch, the animations seem a bit broken too. If you have any resource packs turned on other than the default one, turn them all off; if you have none turned on, turn one on and then off again. After doing one of these things, see if the problem persists.
Your other cats disappearing is a glitch that happens sometimes. Just close the world and open it again, and if the other cats still aren't there, keep trying until it works. If it still refuses to work, I don't know.
As for the "demon" cat not eating any fish, I'm not sure what would cause that. Maybe a behavior pack glitch, similar to the resources glitching?