Increase of "unknown" NAT assignments by probetest since 2021-10-25

https://lists.torproject.org/pipermail/anti-censorship-team/2021-October/000197.html

...looking into the broker graphs there is something weird since 2 days. The number of proxies with 'unknown' type of nat has rised heavily at the same time the 'restricted' nat has gone down. There are long periods without idle proxies and many requests being denied of nat type uknown. It doesn't look like the proxy capacity has gone down, can it be something broken on the way we test the nat type?

It seems that something is going wrong with probetest. A past problem we had with probetest not functioning properly was #40039 (closed). Currently the probetest process is again using 100% CPU.

It is possible this is some kind of slow resource exhaustion, or it's possible that probetest is simply overloaded with the number of proxies we have currently. At the 2021-10-28 anti-censorship team meeting we decided to restart probetest and watch it to see how quickly it returns to its failure state, in order to distinguish these two possibilities.