Where do user utm tags come from in Google Analytics, even months after you removed them from everywhere?

Question

Google Analytics

At one time, I hung an advertising banner on my website leading to the page of the special project. In order to better track the banner click statistics, I put utm tags on it:
— utm_source=site
— utm_meduim=banner
I already realized that it’s better not to do this, since these same tags begin to fray the original referral sources and original channels. Those. if a user went to my site via a link from another site, and then clicked on the banner, then in GA this user will not be counted as the one who came through the referral link, the original source and medium are overwritten by the corresponding values ​​of the banner. But that's not the point.
The banner hung for only a week. But after we removed it, GA still shows "site/banner" in the Source/Feed section. The number of sessions for this source/channel is gradually decreasing, but this happens very slowly. We checked the code of all pages with a search, but nowhere did we find a potentially remaining banner with such tags.
Tell me what does it all mean? And how to fix it?

Answer 1

No fix. People could bookmark it, it could be indexed by bots and search engines. The traffic will go, you can't do anything about it.

Answer 2

I will add another option with prediction in the address bar
. Theoretically, 301 can make the browser "wipe" the old version, because browsers cache this behavior (not in the case of bookmarks)