Several devices for same caldav access

I recently added the nextcloud calendar on my iphone using the existing caldav adress. All working without any problems. However, i found out today that there are many entries in the device section, each for the same calendar (and it is even creating more from time to time). Take a look at the screenshot. Does anybody experience the same and how can i avoid this behavior?

That’s the normal behavior of the function, because it works as an access log for your app specific account. The systems automatically cleans-up old entries after a while. So don’t bother and keep enjoying Nextcloud.