Hi, I can see how losing those calendar icons makes tracking invoiced jobs harder, and I want to help get you back on track. the root cause is a recent outlook on the web update that removed support for the legacy event icon renderer, so existing events still hold an icon value but the UI no longer displays it, which is why you see a blank.
First, try basic steps to rule out a cache or extension issue for the new UI code path refresh, clear browser cache, test in a private window, and try another browser. check whether you’re using the new Outlook toggle and see if the behavior changes in classic vs new. As a workaround, use categories with colors or add an emoji like a dollar sign directly in the event title, which continues to render. If you can, test creating a brand new event and applying an icon to confirm it still shows blank. A few quick questions to pinpoint this are you on Outlook.com or microsoft 365 work account, does the issue happen across browsers and devices, which outlook experience are you using new or classic, and do category colors still appear correctly. If you share those details, I can guide you to the best path forward.
Chard