[C#] Microsoft.Graph.Entity (version 3.8.0) case sensitive fields in AdditionalData dictionary casing changed since this morning

Question

We currently use v3.8.0 of the Microsoft.Graph NuGet package in our function app to call the Graph API to return data from B2C tenant users.

Some custom attributes we set are present in the Entity.AdditionalData Dictionary field. These fields have always been named extension_{applicationId}fieldName.
Since exactly 7am EST this morning these fields are now being returned as extension{applicationId}_FieldName, with an uppercase F. Because Dictionary keys are case-sensitive in C#, this caused the application to stop working until we found this cause.

No changes were made anywhere in the application or on the B2C tenant. We did not update the NuGet package either. Calls to the data using Azure AD Powershell still return the old casing. I cannot find any entry about this in any of the changelogs.

Is there any explanation to this sudden change in the way the Entity.AdditionalData field is populated? Was this an intended change to the MS Graph API?