Just decided to solo run a Helltide that was halfway done after hearing the doom and gloom nerfs that have ruined peoples enjoyment of them. Farmed 500 cinders in 26 mins and got 2 chests and was happy with my run. I didn't find the cinder drop rate to be nerfed but obviously the difference from needing an extra 75 cinders for a mysterious chest is a big increase. Getting 4 mysterious chests in an hours run is very achievable from my experience.