To reproduce:
ITableEntityGetEntityAsync<TableEntity>(pk, rk) - note the etag is correct.GetEntityAsync<YourCustomEntity>(pk, rk) - note the etag represents null.Examples:
Using TableEntity:

Custom Entity:
Here is the result:

Here is the entity:

Environment:
Thank you for your feedback. Tagging and routing to the team member best able to assist.
Thank you @kieronlanning! This was a regression introduced by https://github.com/Azure/azure-sdk-for-net/pull/16315.
@christothes No probs! Do you know when the next release will be?
We typically release the second Tuesday of each month. If you'd like to get the bits sooner than that, you can grab them from the nightly dev feed here
Wicked, I'll do that. Thanks @christothes.