Navigation- and text-inserted Hyperlinks disappear — Sharepoint Online

Hi everyone!

I'm facing the following issue in SharePoint Online:

When linking external pages (on an old SharePoint 2016 or on Engage) in the navigation or in the text of a news article (etc.) some of those links disappear after a while and when we try to re-insert the link, it doesn't get saved at all. At first we resorted to creating a new nav point and inserting the link there (which then worked) but this just isn't sustainable. Apart from that, hyperlinks in texts just unlink themselves and have to constantly be redone. 

I've read on here that in some cases of MAC users the links may contain the characters %E2%80%8B, which when removed solved the issue, however we don't use Macs and haven't found those characters in the links yet.

Does anyone happen to know what this might be and how it can be solved? 

Thanks,

Sarah