According to a wireshark it looks like PRTG is doing a lookup on OID:
Doing an SNMP walk on the 18.104.22.168.4.1.2021 OID with the PRTG SNMP tester there is no 22.214.171.124.4.1.2021.9 OID tree. it goes from the 126.96.36.199.4.1.2021.4 tree then skips to 188.8.131.52.4.1.2021.10 tree.
PRTG returns error 222 on the sensor.
CPU and Memory sensors work. Only disk utilization via SNMP doesnt.