I work with a 25% wbv potassium Oxalate solution, and develop at about 65C. Crystals form in the bottom of my storage bottles when it cools overnight, but not during print processing. The temperature drops when I pour it onto the print by 10-15C but this isn't enough to form crystals.

Hot developer can strip out material from the paper. I've found, for example, that the gelatin in COT320 makes the developer slushy after a while. If this happens then simply filter the developer through a coffee filter to clean it up.