Villagers Randomly Switched Profession

I was Doing Some Other Things in my Minecraft world and came back To my village to find that around 90%  of my villagers changed Profession And that some Villagers that somehow Never got a profession no matter how hard i tried. its a bit frustrating since i spent alot of time trying to upgrade the level of my villagers. theres no real way to get back the levels other than earning it back but i dont want this happening to me or other players again. Thanks for reading!