Everything from hot weather to bug bites to pain itself. We can't end all of it.
Um, those can all theoretically be solved with sufficient level of (bio)technology, even sticking to the limits of purely hard science fiction, within the limits of the laws of physics. So that would just assign minimum technological requirements for any true utopia, not disprove the possibility of it.
For example, personally, I wouldn't totally remove the capacity for pain (because that might eventually cause some form of sensory deprivation, or some other potential unwanted psychological side effect), but build in a ceiling threshold (because after a certain point of intensity, the level of pain humans are capable of feeling serves absolutely no useful psychological or warning system purpose any more) and give people a mental on/off toggle switch for what capacity for sensible level of pain remains.
What you really want to talk about here, is
emotional suffering. True, a lot of things, like clinical depression, are chemical and can be resolved with sufficient technology, but you can't remove the pain from, lets say, a heartbreak over a breakup, without also changing how humans love, which sounds more dystopian, than utopian.
Then again, I don't think that removing absolutely
all forms of suffering like that is a fair criteria for an utopia in the first place. Without
some capacity for suffering, people wouldn't also be able to
enjoy some things, like BDSM or horror movies/games.
So I think the better criteria would be, that a hypothetical perfect utopia must enable to remove all
unwanted suffering, that people wouldn't, individually, find to possess some desire to remain capable of feeling.