In an Exchange 2016 environment, your organization has lots of Accepted Domains. MSExchangeOWAAppPool application pool may consume a very large amount of memory every time that it recycles on schedule or manually.
Additionally, the MSExchangeOWAAppPool application pool is marked as unresponsive by Health Manager and the Outlook Web Access (OWA) client might be unable to connect to OWA.
This issue occurs because many threads are trying to retrieve all accepted domains at the same time and memory has to be allocated for each thread to perform the job.
Cumulative update information
For Exchange Server 2016
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.