[Baertram]

It's only a guess.
One would have to check the addons, which functions they use in common, or which EVENT_* they use in common to detect the item was listed via AGS e.g.
Maybe sirinsidiator knows more about this at AGS (he already noticed it as well, and we are waiting for feedback of ZOs).
In the end it must be server handled I'd say, read below:

Roomba e.g. is checking for the guild bank to be ready and then withdraws an item, stacks it in your player inventory and tries to deposit it again.
If the deposit worked, it will withdraw the next. So I assume the deposit somehow needs that long sometimes and thus it's waiting.

If both addons now got a similar waiting time it cannot be a conincidence so I assume it's server driven somehow. The reason: I guess it's a performance improvement approach as ZOs works on many performance improvements (buffs, guild history, etc.)