I’m having the same issue, when the sequence was under 6 minutes long i could render out anything i wanted, then i added more content and stuff started getting bad… thought it was my ram, my drive, my cat… i guess its just bad code. my sequence is over here, https://captainhookup.com/3ac/alphabet_animals.html each animal is a separate motion file… but i guess its too much for the mac to handle… but hard to believe.