I don't have any apps that can turn off the Wi-Fi itself, but even if my Wi-Fi router (at home) is fine, it just to turns the Wi-Fi off automatically on my phone. This has happened a few days ago, and my phone is up to date. Regardless, nothing is in "Wi-Fi control history", and I don't have the "Wi-Fi power saving mode" option. I don't know what could be done in the developer options, but if you have a clue, please let me know.