question about trials of chaos boss rotation

Is it random every time? Do we get a set rotation every day? I've just ran 7-8 trials and each and every one has had the plague boss first, bird boss second and chimera third. So I've only gotten cowardly fates 7-8 times in a row. Not sure if I'm doing something wrong because the last time I ran trials in bulk I was getting different boss rotations every run.