In trying to resolve some of their latency issues for their Linux client (on Github) I realized everything was being funneled through Neustar, which was the issue. So I questioned them about it, and they confirmed it.
The other service was Radware. The problem some people had was not the tech (it uses GRE tunnels that doesn't compromise our TLS), but that Israelis are allegedly shady. We don't think that's a fair characterization. We have switched from Radware for other reasons in 2018.
There is a particular leaks site that also called out Proton for routing their connection thru a similar shady service in the past.