Both apply

The ordering of which bend luck applies is determined by the person whose turn it is (per Xanathar's Guide to Everything), but that is irrelevant because addition is commutative.

Combining magical effectsCombining magical effects section does not apply

...apply while the durations of the effects overlap...

There is not durationduration for bend luck, so. The effect instantaneously adds or subtracts from a roll. So that section does not apply here.