TiN,
What's strange is the continuous negative drift.
If the resistors R4, R5 (10k) inside ASIC are not correctly matched (any more), I'd expect the +12V reference and 10V reading going up and down with temperature.
It may also be possible, that U165 is damaged, like excessive input bias, or so.
But I lost overview, which ASIC is now on which PCB..so if this failure went with the ASIC, it's not so probable.
Frank