Hypertext links to external targets sometimes become "fragmented". It means that one link on a word or a phrase falls into more pieces. Each of these pieces holds one link which can be manipulated separately and which has its own <a> element in HTML export. Steps to reproduce: 1. Write some text. 2. Select a portion of the text. 3. Create a hyperlink on the selected text. 4. Do some other edits on the document. But the described behavior is nearly irreproducible due to its indeterministic nature. It occurs only occasionally and I can't trace any relationship to other operations.
One naive way to get such a result is to insert a paragraph mark inside the hyperlink text then delete it. Of course I suppose that your other edits on the document don't include such operations.
Those "other edits" don't include such operations of course. They don't include any operations at the hyperlinked phrase at all.
Dear Lukas, Thank you for filing the bug, but unfortunately without clear steps to reproduce it, we cannot track down where the problem originates from.