I'm having the same issue as well. I had to stick a small fan on the case for now.
Under load, the frequency never drops below 1104MHz.
I'm a bit of a noob but I've been trying to investigate (so let me know if I'm way off).
houldsg@orangepipc2:~$ uname -a
Linux orangepipc2 4.19.20-sunxi64 #5.75 SMP Fri Feb 8 10:29:25 CET 2019 aarch64 aarch64 aarch64 GNU/Linux
houldsg@orangepipc2:~$ cat /sys/devices/virtual/thermal/thermal_zone0/
available_policies cdev0_weight k_d k_pu policy subsystem/ trip_point_0_hyst trip_point_1_hyst type
cdev0/ emul_temp k_i mode power/ sustainable_power trip_point_0_temp trip_point_1_temp uevent
cdev0_trip_point integral_cutoff k_po offset slope temp trip_point_0_type trip_point_1_type
houldsg@orangepipc2:~$ cat /sys/devices/virtual/thermal/thermal_zone0/trip_point_0_temp
65000
houldsg@orangepipc2:~$ cat /sys/devices/virtual/thermal/thermal_zone0/trip_point_1_temp
90000
65 degrees is when the frequency drop to 1104. Does trip point 0 trigger a particular frequency (1104)? Should there be more trip points or is the throttling handled by another mechanism?