As other answers have mentioned, I think one of the big struggles is people not fully understanding what a UX designer’s role is or is supposed to be.

Some of the big complaints I’ve seen:

• People thinking UX is just a fad or a passing trend
• UX design is another way of saying graphic design
• UX design is all about innovation and breaking the mould - it’s not, it’s often about using tried and tested conventions

But in my opinion, probably the most frustrating thing is coming up against people who dismiss UX research all together, saying “we don’t have time” or “we can’t afford it.”