I’ve never seen or heard of this happening. But only yesterday I was looking at my bike (while sitting in the train) and marveling at how thin and fragile those front derailleur linkages look ;)
I can’t think of anything which would cause this, except an impact or crash which might not have broken it immediately but weakened it enough (possibly also bending it slightly) for it to break later during normal use. Shifting under extreme cross loading and with lots of force on the pedals would probably lead to the biggest (sideways) loads on the derailleur, so that should be avoided. But I think usually you’d struggle to push the shift lever hard enough to cause any damage that way. I did break some left brifter pawls that way on a Shimano 105 5700 STI brifter but the Shimano CX70 front derailleur it was connected to keeps working 10 years later.