Unexpected error on Opening of custom entity record

Hi Experts,

I have one custom entity and its subgrid is on Opportunity entity. I have a ribbon button on opportunity to create record for custom entity.

1. I click on ribbon button and create new record.
2. save and close newly created record.
3. Record appears inside subgrid.
4. Now click on that newly created record and it shows unexpected error.

I tried disabling all plugins, javascript running on that entity still same issue. 

Issue occurs only if I open record from subgrid on Opportunity. If I just refresh the record, or reload, error doesn't come.

Error details:

Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: System.NotImplementedException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #9DF1D73ADetail:
<OrganizationServiceFault xmlns:i="www.w3.org/.../XMLSchema-instance" xmlns="schemas.microsoft.com/.../Contracts">
<ActivityId>1a394149-9346-4453-b9bd-10ca4c9c6b49</ActivityId>
<ErrorCode>-2147220970</ErrorCode>
<ErrorDetails xmlns:d2p1="schemas.datacontract.org/.../System.Collections.Generic" />
<Message>System.NotImplementedException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #9DF1D73A</Message>
<Timestamp>2018-12-14T10:13:57.4160556Z</Timestamp>
<ExceptionRetriable>false</ExceptionRetriable>
<ExceptionSource i:nil="true" />
<InnerFault i:nil="true" />
<OriginalException i:nil="true" />
<TraceText i:nil="true" />
</OrganizationServiceFault>