We’ve recently come across an issue where the Dynamics 365 App for Outlook would freeze and stay stuck in the ‘Loading’ screen. It took us a while to figure out exactly what was going on, but after a lot of searching, swearing, coffee drinking and praying to Bill Gates, we managed to find a pattern;

Here’s how the issue can be reproduced:

  1. Open up the Dynamics 365 App for Outlook.
  2. In the app, select a record and click ‘View in Dynamics 365’.
    Dynamics 365 App for Outlook - View in Dynamics
  3. In the new pop-up, simply press F5. Your screen now stays stuck in the loading screen as shown below.
    Dynamics 365 app for Outlook - stuck in loading

What’s causing this?

We couldn’t find a logical reason ourselves. We tried numerous things like:

  • disabling customizations,
  • trying it out on a trial environment,
  • trying it out on our customers’ environments

Unfortunately all of the environments showed the same behavior. We ended up opening a ticket with Microsoft Support, who’ve confirmed that it does seem to be a bug on their side, related to a ServiceWorker running in the background.

So how do I fix it?

It turns out that one of the famous ‘FCB’-settings is causing this behavior… the FCB.UciServiceWorker to be more specifically. Although you could disable this setting yourself, I would strongly recommend contacting Microsoft Support and have the disabling the setting for you. Once Microsoft Support updated the setting, our Dynamics 365 App for Outlook worked like a charm. They have also confirmed that this issue will be resolved within the next release.


What is this FCB Setting you are talking about?

FCB Settings is short for Feature Control Bits. These settings control some of the features within Dynamics 365. Generally you shouldn’t be touching them yourself, but if you really want to experiment with this settings, I strongly encourage you to read this blog post.