Hip pain out of the saddle
I think this hip pain is an indication of fatique, which will diminish through ptactice.

I experienced this once.  

I had been cycling for more than 20 years and was skillful with out-of-saddle ride.  I did this every now and then for say less than 1 km for fun.

Last September I challenged myself to a total of 10 km climbs (8 discontinous climbs stretched over 36 km) out of saddle. The gradients varied from 5 to 10.

The following morning my hip joints hurt.  Then I realized it was fatigue.

After a week I rode the same route again to test.  This time there was no more fatigue.  

I think practise and rest and practise, and the pain will go.  My experience.