I also lost the Xoutpost app when I was having trouble with my Android phone, back in April.
Suddenly, my Samsung S9+ could receive calls or internet, but not both at the same time, so I worked with Boost Infinite techs for over a week until we found a solution (three complete reboots, two new APNs tried, a new sim card, and 24+ hours on the phone).
When the phone returned to normal, I had to reconfigure my phone, including re-installing all my lost apps and widgets, but I found that the Xoutpost app wasn't available, anymore. I tried to contact the admins of XO,
https://xoutpost.com/1238126-post1.html, but got no reply from them...probably because "
Xoutpost is currently undergoing a planned server migration.... stay tuned for new developments.... sincerely, the management".
So, I reinstalled Tapatalk (free), and was able to use it to see XO on my phone again, but since I've had a love-hate relationship with Tapatalk for many years (during which I've installed/uninstalled it many times, on several devices, for three reasons...fails to connect, freezes up, uses too much data in the background), I also made a Google shortcut to the XO "E53" page, to sit ready for use, on my homescreen, as a back-up.
Perhaps I'd get better service from Tapatalk if I bought the paid version, but as I said, I don't rely on their app, entirely.
Does anyone know why the XO app was withdrawn from the app stores?