Sounds like you have upgraded the main firmware to 1.19 but not the WiFi firmware. The upgrade to 1.19 is different from most firmware upgrades. See https://duet3d.com/wiki/Upgrading_to_DuetWiFiFirmware_1.19.
What you need to do now is create the /www folder (or delete all files and directories from the old one) and unzip the DuetWebControl files to it, also copy DuetWiFiServer-1.19.bin into /sys and rename it to DuetWiFiServer.bin. Then send M997 S1 from USB or PanelDue to install the new WiFi firmware.