It might be that your iMac cooked the SSD.

I had one in mine ever since the 1st beta supported it (so a few years) and in past few months I got rare to ever more frequent errors at start.
A few days ago I moved another SSD in there which gave 0 problem sofar.

I haven't found the time to check the old one for SMART status in a "modern" computer so I can only guess that it is combination of MorphOS not handling SSD health and extensive heat in the iTight_G5.