You are using an object $tbox from across threads. This does not work.

You can use threads and Tk in the same app, but you must confine all your interaction with Tk to your main thread.

If you want to use information collected or generated in your other thread(s), to be displayed in your Tk widgets, your must communicate that information from the other threads to the Tk thread through shared variables--scalars, arrays or hashes; not objects.

A good way to communicate strings that you want to display in your textbox woud be to have your comms thread enqueue them to a Thread::Queue, and have your -after routine dequeue them in your main thread and update the display.

Do a supersearch for "threads" & "Tk", with my name as the author and you should find one or to examples plus some explaination kicking around.