I can't do any damage

I recently made a server and when I got on it with my friend I found that I could not hit anything. I can break blocks but I can't hit any mobs. It is not the modpack because I've tested to see if it was twice in different worlds it's only when I play on the server that this happens. I have checked to see if I had the wrong keybinds and correct game mode everything seems to be alright I don't understand why I cannot hit anything. My friend and I found out that if we died, we were able to attack after that, but after I had changed something minor, it messed up again and no matter how many times I restarted the server or how many times we killed ourselves, we couldn't hit anymore after that. Any solutions?

Also, I doubt it is lag there is no lagging on the server it runs pretty smoothly it's just this one little bug is messing up the whole experience.

I use Forge and as I said previously I don't think it is the mods/plugins because like I said I have used them in a different world twice before, it is only when I get on my server that this problem occurs. They work fine together. Unless there is something specific on the server itself that makes it to where it won't work correctly with specific mods? But I don't know why the mod would be available if that were the case.

Sorry, I would but I just decided to make a new server. Hopefully, it works now if not I will get back to you. I will say this though just in case it doesn't work. What I had changed was my friend's origin. We had origins and she wanted to change hers so I changed it and afterward it just wouldn't let us hit anymore (When we had started it already wasn't letting us hit, we had to die for that then it started working and after I changed her origin it wouldn't let us hit again). After leaving it for a while when we got back on we realized we had to keep constantly dying in order for us to be able to do damage because once we died we'd be able to do damage again but then it'd stop working after a while so we would have to die again and keep repeating that process.