ER-4XR in 2016 with one side crackling, got it replaced but the shipping to America was almost as expensive as a new pair... my current ER4-SR has a loose connection in one of the drivers but its not so serious
but other than that, the usual bass tolerance that I can hear but apparently is acceptable to everyone else (and also technically within spec of the ER4 series since the matching only goes down to 100hz), the most egregious being the ER3-XR I had in 2019, the bass was so off-center that it was borderline nauseating to me... I had to make a passive filter circuit board to electronically control the sub-100hz region to each driver manually
https://www.head-fi.org/threads/passive-headphone-attenuator-with-bass-bypass.945585/post-15941391 , and I am using it with my current pair of ER4-XR's because the side with the loose connection also has too much bass, as well as a much higher sensitivity to AC hum