Update 4/23/2024: We have now released April 2024 Hotfix Updates which address known issues in March 2024 SU updates.
Microsoft has released Security Updates (SUs) for vulnerabilities found in:
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Updated Apr 23, 2024
Version 8.0
Blog Post
"We believe that we have identified the problem causing this. It is related to a service side change that was just timed similarly to when release of on-prem updates were released but is completely unrelated to Exchange Server CU or SU updates. Rather, it is related to a Cloud Cache service side (see how this works here: https://learn.microsoft.com/en-us/exchange/clients/outlook-for-ios-and-android/use-hybrid-modern-auth?view=exchserver-2019). We are working with the relevant service team to address. We are still investigating the details of this but this would explain exactly what is going on."
We are also experiencing this now. No workarounds listed in the comments have worked. Is there an ETA for a fix for this?