In particular, the claim that tesonet controls protonvpn's release signing key.
https://news.ycombinator.com/item?id=17258203
https://news.ycombinator.com/item?id=18611863
It seems very likely now, that ProtonMail just decided to use NordVPN's white-label solution to bootstrap its ProtonVPN business:
https://nordvpn.com/white-label/