You're writing in the AR mixer's section...
Using the line input on the SL AI series mixers deactivates the microphone preamp, so it's either or. The line input will "kill" the XRL input. You don't need to unplug the XLR connector, but to keep your set-up organized it is always better to use 1 cable for 1 connection... If you need to search for the reason of a problem, double connections are not really helpful. Using the inserts works, but the line in - technically seen - is the better choice. Keep your set-up simple. Use the preamps and send their line signal to the board. Remember that the line inputs of your mixer are balanced (symmetric TRS).