It looks like the 'unkown' NAT proxies are going up pretty fast while other NATs go down. I got into the server, but I don't see it being overloaded or any obvious problem. I restarted probetest, let's see if it gets back to normal.
Quoting alertmanager@hetzner-nbg1-02.torproject.org (2022-04-05 19:06:44)
Total firing alerts: 1 Total resolved alerts: 0
## Firing Alerts
Time: 2022-04-05 17:06:00.286335746 +0000 UTC Summary: There is a problem testing the type of NAT of our proxies Description: There are only 1.8 times proxies with known NAT type than with unknown
##Resolved Alerts