It's not an "issue" — there would be an issue if links weren't built this way!
In HTML, the ampersand (&) character has special meaning: it's the character at the beginning of a character reference. You've seen such references as © or ‍ in the past, I'm sure.
In order to avoid breaking links, whenever you want a a literal & — that is, where you aren't using it to start off a special character reference — you must use its own character reference, which is &. This means that what you think of as a run-of-the-mill URL like
https://www.example.com/?utm_medium=email&utm_campaign=myCompaign
when it appears in the href of an <a> tag, should be written:
<a href="https://www.example.com/?utm_medium=email&utm_campaign=myCompaign">Click here</a>
Note that the URL as sent by the browser doesn't have the & in it. The & is necessary only within HTML, to make sure the link is rendered unambiguously. Again, you'd never type & in the browser bar, it has no special meaning there and you'd mess things up in the other direction!
You're probably thinking. "But I don't think my links have ever been broken...." True, you might've gotten lucky so far. But to give you an idea of how a link can be broken without & imagine you're trying to get people to the URL:
https://www.example.com/?audience=global€germany;berlin
If you put that in an href as-is:
<a href="https://www.example.com/?audience=global€germany;berlin">test render</a>
The link will be broken, because you've accidentally included a character reference: € is the character ref for the Euro symbol! So people will end up on the wrong page (probably a 404):
The correct way to link to that URL in HTML is indeed:
<a href="https://www.example.com/?audience=global&euro;germany;berlin">test render</a>
