Ha ha! My Tenno is just MR 5, but I guess my Nightwave standing is sort of high. Apparently, if your Nightwave standing is high enough these guys show up to ruin your mission. https://warframe.fandom.com/wiki/Zealot_Proselytizer (Zealot Proselytizer) I ended up failing a mission because of their shenanigans, but I was ready for them on the next missions. In fact, they have showed up on every spy mission above level 8. Thankfully, I've been upgrading my Tenno mods, so that helped.