It does sound as though there is a serious problem on the opto cells.
If you want to have a go at it yourself, on that model (SC2.2) the opto cells can be replaced with standard ORP12 cells. You can break away the glued opto covers to get at the cells. Strictly, they should be matched.
If you want me to fix it, that’s OK; for Joemeek equipment it’s a nominal £25 plus the cost of returning the unit to you. Email me at email@example.com