Items keep disappearing out of my hotbar.

So, whenever I'm holding a book or something in Minecraft, the book or item just disappears out of my inventory. It's kind of irritating. I have mods installed, and I'm not so sure if it's a bug with the mod or if it's a 1.17 glitch. Maybe you can check anyways? It's only the item that I'm holding in my hotbar, and I kind of had enough with it after I was writing an 8 page rule book and it disappeared. If it's an actual game bug, can you please fix it?