When trying to add bits to a work item in a way that will get rejected (bits below working temp, work item too tall, work item below working temp), the user attempting the process will crash rather than receiving the expected error message on screen.
This is using vintage story 1.21.5, scientific smithy 0.1.6, and smithing plus 1.8.3. There are additional mods on the server, but scientific smithy was the only mod added before this issue began, so it's expected to be the cause. I can perform additional local testing if it can't be replicated.
An identical issue has been created on the scientific smithy issue tracker.