Many routers do not rehash everything when a link breaks.
Doing so would disturb flows that were not broken, causing possible
misordered packets or jitter.
The flows on the broken link will get rehashed, of course.
Note that even if a hash function can distribute the flows evenly,
you may get some heavy flows, so you need to expect some imbalance.
It will work fine if you have a good modern router. Consider this; all evenly grouped LAGs are odd in their failed conditions.