Mortar-bedded ridges
Cracked pointing is not always the same as failed bedding. A ridge tile may look rough at the edge yet remain secure. If it actually moves, loose material needs removing before a proper repair can be made.
Dry-ridge systems
Modern systems use screws, clips and connectors. Adding mortar around a failed dry-ridge component does not restore the mechanical fixing. Identify the system and repair the part that has come loose.
After a storm
Fragments of mortar on the ground can be an early sign. Look along the ridge from safe ground for a tile standing proud or a gap that was not there before. Keep away from the area below a visibly unstable piece.
While access is in place
If one section has failed, check the rest of the ridge line. That can be done without inventing unnecessary work. Photographs of sound sections are useful too.