Alright, so after "a while" (not sure what exactly causes it), it seems to happen when switching worlds for the first time. (after leaving your homeworld).
The bug seems to be that the "Timed out for spam 30 secs remaining" message appears when it normally wouldn't. You can still send OSC messages to the chatbox when the timed-out message pops up; however, once it first appears, it seems to show up for every subsequent message you send, regardless of the time in between the messages.
The bug also seems to cause other weird issues to happen. Sending an empty string has an interesting effect and is actually how I first noticed the issue. When this bug is happening, sending an empty string doesn't make the chatbox disappear. It does, however, cause any message you send after it to instantly disappear after sending for a couple of seconds. (So, if you are rapidly sending messages to the chatbox, it will appear to flicker or blink.)
If anyone has more solid reproduction steps or other effects of the bug please feel free to add.