They are time-bombs. Why? Yes, they have even wall thickness, the glaze is not crazing and the clay is vitrified. But, they are glazed only on the inside and that is a problem here. The glaze is under some compression, that is why it does not craze. That means that it is pushing outward from the inside. Ware can be very strong under glaze compression, but only to a point. When a hot liquid is poured into containers like these the inside glaze is the first to thermally expand, creating more even compression. The porcelain is under tension already, being stretched by pressure from within. And ceramics do poorly under tension. And third: The outer surfaces have incised lines that provide irregularities for internal forces to exploit and start cracks at. It is a perfect storm waiting for hot water to trigger it. Making the pieces thicker would help. Increasing the glaze thermal expansion would help. But unglazed outsides and incised lines will always be a weakening factor.
In ceramics, glazes are under compression when they have a lower thermal expansion that the body they are on. A little compression is good, alot is bad.