Thank you for your response.
Yes, I am using version 3.1.0:

<PackageReference Include="MongoDB.Driver" Version="3.1.0" />

Looking at the driver’s code at mongo-csharp-driver/src/MongoDB.Driver/TransactionExecutor.cs at fc052f42455e8ed6d4c648a178fca272fdb8d181 · mongodb/mongo-csharp-driver · GitHub,

it’s clear that the issue will indeed occur.
The errorLabel is only being checked on the main exception, not on the inner exception.