I had a devil of a job on a replacement Genesis i0 frame. Never had the issue before in 15yrs of MTBing, tried various seat posts (they all vary slighly around the manufacturing tolerance), I tried heavy duty downhill seat clamps, I was going to try an oversize seatpost (27.3 instead of 27.2), in the end a shim made from a coke can wrapped around the seat post solved the problem and never had an issue since. Mind you, I probably won’t be able to get it out again 🙁