Yes, a complete reset could become a desaster... Let's try to narrow this down. "Line Gain" is shown automatically, when a line signal (keyboard, guitar, CD player etc.) is inserted in the combo jack. Your channels 17 to 32 have combo jacks (XLR/TRS). When you pull the line cable out, the channel is automatically set back to "PreAmp" (Gain).
I guess there still is a wrong cable sticking somewhere...