@Superpiffer Do you think it will work if I change to below

if (tf.Status == null || tf.Status.Handle.IsInvalid)
{
    c_api.TF_DeleteSession(handle, c_api.TF_NewStatus());
}
else
{
    c_api.TF_DeleteSession(handle, tf.Status.Handle);
}

@Superpiffer Do you think it will work if I change to below

if (tf.Status == null || tf.Status.Handle.IsInvalid)
{
    c_api.TF_DeleteSession(handle, c_api.TF_NewStatus());
}
else
{
    c_api.TF_DeleteSession(handle, tf.Status.Handle);
}

I think so, maybe that's ok as a "last resort" in my use case, also preserving the previous behaviour. I can test it on monday.
The problem is that I'm not familiar with ThreadLocal and I don't know why tf.Status is disposed before all the session threads are stopped and ONLY on .NET 4.8...

@Oceania2018 I tried and I have the same problem:

Is there any code like using(session.as_default()){ } in your code? Sometimes annoying things happens when I use the scope with using.

Is there any code like using(session.as_default()){ } in your code? Sometimes annoying things happens when I use the scope with using.

No, I cannot use using because I need to reuse the same session during my processing. You can find a sample code here: #912

Also I made a new PR with a possible solution: #978