Have at least three timestamps listed in ascending order.
Minimum length for video chapters is 10 seconds.
Alternatively, just use this app to automatically fix them. It pushed chapter markers forward to give your viewers a better experience. If you have too many small (<10s) chapters consider combining some!
This is not officially affiliated with Youtube. You can see that by how janky it is. If it doesn't work for you, I'm sorry, there are no guarantees this fixes everything, despite my best effort. Use at your own risk.