Players have noticed that Bullions seem to have an unannounced cap of 12 and no new Bullion is available this week.
Dragonflight Season 4 has had a lot of bugs, including being disabled early in June and disabling the Season 4 upgrade vendors yesterday. It seems that another Dragonflight Season 4 bug may have taken place, or an unannounced cap — Bullions no longer seem to be dropping and are capped at 12.
Antique Bronze Bullions seem to be tracked using the hidden currency 10.2.6 Rewards — Personal Tracker — S4 Dinar Drops (Hidden). This hidden currency tracks the number of Bullions you have collected and the current cap. However, since you can't see the currency on your Currencies page, you have to pull the data by using a script. Here's one from the forums by Vennaya:
If you run this script in game, you will see that the current cap of Antique Bronze Bullions seems to not have increased to 13 and remains at 12, despite this being the 13th week of Season 4.
In the Season 4 Patch Notes, no mention of a 12 Bullion cap was mentioned, and that the cap will rise by 1 each week. This seems to contradict the current status of Bullions on live servers.
Now, there's also a hidden currency for tracking spark drops 10.2.6 Professions — Personal Tracker — S4 Spark Drops (Hidden).