I’d say the concerning thing is that they have been staked and still broke.
G.41 and G.935 are definitely known as having their problems - G.41 for weak scions/rootstock attachment and G.935 for being virus susceptible. I’d not be surprised if virus susceptibility showed up as a weak union too.
Here is a curious plot. Note that the two Geneva stocks touted as free-standing trees for processing orchards - G.969 (6969) and G.890 (5890)- have the weakest union strength.
