pls help me

• Post your exact server version (including the build number) (/version output)
• Post your plugin list
• My guess is that maybe some other plugin is interferring. You need to figure out which plugin. Try to reproduce your issue on an up-to-date Spigot server without other plugins and without client-side mods. Then step-by step re-add other plugins until you can reproduce the issue.

I'm having the same issue, it occurs when connecting to a server which is hosted on a newer version like 1.21 and then joining through an older client such as 1.20.6 through viaversion + viabackwards. I brought this up with the core developer of viaversion/viabackwards and they claimed it's a visual bug caused by the shopkeepers plugin.

and they claimed it's a visual bug caused by the shopkeepers plugin.

I will not debug cross-version / protocol / ViaVersion related issues. Unless someone familiar with the issue can clarify the cause of the issue / propose a potential solution, I will not further investigate it.

From simple test:
I think it's a issue from Eco plugin