This is normal. I don't recall the exact battery temp, but above a certain temp and the car will limit the charging and discharging rate of the HVB to prevent damage. You can try to park in the shade during the day as a way to keep the HVB cooler. Also, plug in whenever possible but use a Value Charge profile to delay charging until the middle of the night. Whenever you plug in, the car can use wall electricity to cool the HVB. If you don't plug in, the car cannot cool the HVB. Also, when driving use the air conditioning. The car cools the HVB with air from the cabin. Keeping the AC off results is warmer air in the cabin which means the car can't cool the HVB as effectively.
Hybridbear's post in Engine on because of batt temp was marked as the answer