Thank you for your post.
l'm not able to replicate the issue and haven't seen it for a while. Are you using the latest version (v17.3.0) and can you replicate the issue in a new/different model if you create the joist from the exact same shape (copy and paste it into another model)?
If you can replicate the issue in other models, would you be able to please send the model across to firstname.lastname@example.org
so I can have a further look into the issue?