I just noticed the same thing. I got a notice from Comcast that I was over my data limit this month. Looking through my router logs (Unifi Dream Machine Pro) my pi-hole averaged 5-30 MB of data usage a day until December when it jumped up to 80GB per day being uploaded. I'm going to try taking it offline tonight and see what happens. Any other things I should check and troubleshoot?
Here are the results from my query:
echo ">stats >quit" | nc localhost 4711
domains_being_blocked 1075391
dns_queries_today 190210
ads_blocked_today 3299
ads_percentage_today 1.734399
unique_domains 25448
queries_forwarded 181851
queries_cached 5049
clients_ever_seen 33
unique_clients 21
dns_queries_all_types 190210
reply_NODATA 784
reply_NXDOMAIN 538
reply_CNAME 12487
reply_IP 22784
privacy_level 0
status enabled
Looking forward to learning what's going on here, thank you!