I had an unpleasant experience with Iberia back in 2018. We flew Barcelona-Madrid-London, due to a ground delay on the first flight their system automatically booted us from the second even though we made it to the gate in time. The gate agent was kind enough to re-add us, but then told us "your original seats have been taken (they hadn't been) so just find an empty one". I'm a FA, so being told to pick a random seat and therefore not be manifested properly did bother me. The other thing I raised my eyebrows at was when a smoke alarm started blaring from one of the lavatories during taxi out, and when the FA couldn't get it to stop she placed her jacket over it to muffle the sound...