I have an FTP server on my phone that auto-starts with Tasker to perform unattended backups.
Recently it stopped working. As I debugged the issue I found errors in the log of "unable to connect to wlan0". The Wi-Fi connection was fine, so I was puzzled. I finally re-created the SFTP server profile and discovered that wlan0 doesn't exist. The Wi-Fi connection is now wlan1.
That fixed the problem, but I'm curious why wlan0 would suddenly change to wlan1? No OS updates or new apps have been recently installed.