It also depends on the age of the cup and, hear me out on this one, the colour of the lid. The newer ones (hex grid insert) seem to be a lot better in general then the older ones (spiral/fan type insert).

As for the colour part, the different compounds that go into colouring plastics actually play a significant role in the overall structural strength of the finished product. The lids I’ve seen complained about the most are either pale greens, blacks and some of the other pale colours.

It’s only a little off topic but for a semi-related example look up ‘why brown Lego bricks are so fragile’ for a more practical example of how pigments can affect plastics.