I often reach a deadlock in expert-level hexadoku puzzles. I have checked the solutions and confirmed that my entries are all accurate. Even the x-wing rule doesn't break the deadlock. Are there other special rules or solution techniques used in hexadoku?
You can put your 16x16 sudoku through Sudoku16x16Explainer from here. This uses the same solving techniques as SudokuExplainer. For medium to hard puzzles, the program can be useful. For very hard puzzles, Forcing Chains are extremely slow.