I'm having this exact error after having updated from 2.XX to 2.35. It made me think I didn't clean my saves the right way, even though I did it exactly like in the manual. After 8 tries of cleaning my savefile and encountering that json error I found this thread. Turns out it's not my save files that are wrong, as even with new characters I get this error. That alternate SHESON_DynDOLOD_Firstborn.pex you posted here seems to work for me too, but I'm here to ask if that won't bring any instability issues in the long run, or if I should use a newer version of that alternate file as this thread was from april.