Mackie CR1604 VLZ compact mixer problem

Cutting a long story short I look apart my 25 year old Mackie CR1604 VLZ compact mixer apart to clean the board (I had an issue with channel 15 being all but dead and some crackling on other channels when using gain) and have done so with compressed air etc. and have put everything back only to find all the channel lights are soloed which is strange given when none of the channels are soloed and none of the AUX buttons are enabled.

What could be causing this? I have emailed Mackie Support but I am not expecting a reply in a hurry given Covid-19 and the age of the model.

Wish I’d never taken it apart!

Can anyone kindly shine any light on the situation?

Thanks in advance

The schematic can be downloaded from here if it helps