I have very limited experience, but the few that jump out to me emanate from a few conversations I had with employees during my on-site. For context, the role was for a "Golang / Elixir Engineer" during my onsite all anyone talked about was relatively new code written in Ruby and only mentioned Golang or Elixir in a "maybe 8 months down the road" way. Language barrier with your manager seems innocuous, but the problems I ran into were deeper and seemingly cultural. (she expected to only be told things were going right, nothing was ever her fault, asking for help is indicative of weakness or incompetence etc. - I'm trying to not sound racist but other employees had similar comments)

Also, it took me quite a bit of time to work through the mental gymnastics as to whether I was just bad at my job or if I was in a toxic environment. In hindsight it was definitely toxic - as an example senior engineers on my teams were being put in a position where they had to make decisions TPM's should be making (but still hung out when they made the wrong decisions).