Hi, I meet the same problem as posted here. I checked the value of the results after the multiplication of the two scores (computed by softmax), and sometimes it did gives values larger than 1. It seemed truly a precision problem.
I check the solution of a GitHub repo (https://github.com/NVlabs/wetectron/blob/master/wetectron/modeling/roi_heads/weak_head/loss.py 8). The solution proposed in this repo is simply clamping the scores. I think clmap the values will cause zero gradient during back propagation, but it seems there is no other solutions right mow.