Dynamics 365 V9.0: unable to decode the error log

Question

I am facing issue with all the plugins in the production as they all are failing with below log.

    Unhandled exception: 
Exception type: System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]
Message: Expected non-empty string.Detail: 
<OrganizationServiceFault xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/xrm/2011/Contracts">
  <ActivityId>xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx</ActivityId>
  <ErrorCode>-2147220989</ErrorCode>
  <ErrorDetails xmlns:d2p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
  <HelpLink></HelpLink>
  <Message>Expected non-empty string.</Message>
  <Timestamp>2019-07-29T12:36:40.3815746Z</Timestamp>
  <ExceptionRetriable>false</ExceptionRetriable>
  <ExceptionSource i:nil="true" />
  <InnerFault>
    <ActivityId>xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx</ActivityId>
    <ErrorCode>-2147220970</ErrorCode>
    <ErrorDetails xmlns:d3p1="http://schemas.datacontract.org/2004/07/System.Collections.Generic" />
    <HelpLink i:nil="true" />
    <Message>System.ArgumentException: Expected non-empty string.
Parameter name: settingName</Message>
    <Timestamp>2019-07-29T12:36:40.3815746Z</Timestamp>
    <ExceptionRetriable>false</ExceptionRetriable>
    <ExceptionSource i:nil="true" />
    <InnerFault i:nil="true" />
    <OriginalException i:nil="true" />
    <TraceText i:nil="true" />
  </InnerFault>
  <OriginalException i:nil="true" />
  <TraceText i:nil="true" />
</OrganizationServiceFault>

As this is a limited message, I am not sure where to look.

Update 1: Earlier plugins were successfully executing, all of sudden it starts throwing exception. and I dont know where to find the field settingName, because this field is not there in any plugins or in any entity.

Update 2: Entity List: - Contact - Appointment - Task - Phone Call - CustomActivity

All the Plugins are registered for Post-Operation on either Create or Update Event

Answer 1

We had a priority ticket opened with Microsoft for this issue. We got the RCA from them saying as

Recent weekend deployment - Async machine went in invalid state and failing to deserialize the async context. They restarted the imapacted machine.