Skype For Business - Mobile On Android 10 Can't Connect To Exchange

We recently had several users get new phones with Android 10 installed, or update their existing handsets to Android 10. When trying to view or join meetings from the Skype For Business (SFB) mobile app, it would fail when trying to connect to Exchange.

Some users get prompted for creds over and over, some users get an error "we can't connect to Exchange right now", some users connect but just get a message saying "your meetings will appear here".

Apparently Android 10 includes a change that forces TLS 1.3, but doesn't fall back to older TLS versions. It then gets stuck on the Exchange auth part, which you can see in the client logs: it makes the initial connection to SFB, and then throws obscure "ID_4" errors when it switches over to the Exchange EWS service.

The fix is to disable TLS 1.3 on your load balancer.

I run a Kemp Loadmaster so I'll use that as an example:

Navigate to Virtual Services and select View/Modify Services.

Next, click Modify to the right of your Exchange 2016 VSs.

**Note** You'll want to modify both Internal and External services:

Next, Expand SSL Properties and for Supported Protocols, uncheck the box TLS 1.3:

The change will take effect immediately.

Now hop on to an Android 10 device, and you should be able to open your meetings tab!