A few people seem to be misquoting this thread. Note that the problems highlighted here pertain only when chaining with the Disorder family with the skills "Freezing Showers" and "Cloudless Rain." Both "Zekken - Sudden Downpour" and "Zekken - Twilight Rain," which chain with the QH family along with Tidus, 7* Lightning, and 7* Queen, do not have this problem.

This seems to be due to Kurasame having some type of casting delay when using Freezing Showers.

I noticed this when I was trying to OBAMA Calcabrina with Kurasame. Whenever I would try and T-cast to FTKO the first phase, I was getting 3 sets of 19hit chains instead of a single 59hit chain. This is also the case with his other AOE chaining skill, Cloudless Rain.

Here is a video show-casing what's wrong with Kurasame's Disorder chaining.

I felt like these breaks shouldn't have been happening, since I remembered Prompto's Ballistic, which is also Disorder frames, would get a full chain in Ignis' KM event. So I tested the entire Disorder family on the dummy and lo and behold, Kurasame is the only one that's broken.

Comparing the skills data between all of the skills in the Disorder family, we get:

"228332": {
"name": "Zekken - Freezing Showers",
"compendium_id": 3842,
"type": "ABILITY",
"active": true,
"unique": false,
"rarity": 6,
"cost": {"MP": 45},
"attack_count": [10],
"attack_damage": [[10, 10, 10, 10, 10, 10, 10, 10, 10, 10]],
"attack_frames": [[42, 47, 52, 57, 62, 67, 72, 77, 82, 87]],
"effect_frames": [[0, 0, 0]],
"move_type": 4,
"motion_type": 8,
"effect_type": "Default",
"attack_type": "Hybrid",
"element_inflict": ["Ice"],

"221400": {
"name": "Ballistic",
"compendium_id": 2198,
"type": "ABILITY",
"active": true,
"unique": false,
"rarity": 8,
"cost": {"MP": 25},
"attack_count": [10],
"attack_damage": [[10, 10, 10, 10, 10, 10, 10, 10, 10, 10]],
"attack_frames": [[42, 47, 52, 57, 62, 67, 72, 77, 82, 87]],
"effect_frames": [[40, 45, 50, 55, 60, 65, 70, 75, 80, 85]],
"move_type": 4,
"motion_type": 2,
"effect_type": "Default",
"attack_type": "Physical",
"element_inflict": null,

"703700": {
"name": "Disorder",
"compendium_id": 926,
"type": "ABILITY",
"active": true,
"unique": false,
"rarity": 7,
"cost": {"MP": 25},
"attack_count": [10],
"attack_damage": [[10, 10, 10, 10, 10, 10, 10, 10, 10, 10]],
"attack_frames": [[42, 47, 52, 57, 62, 67, 72, 77, 82, 87]],
"effect_frames": [[40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 40, 60, 80]],
"move_type": 4,
"motion_type": 2,
"effect_type": "Default",
"attack_type": "Physical",
"element_inflict": null,

Ballistic has identical motion_type and effect_frames as Disorder and they chain perfectly together, so I would assume these are where the problems are.
EDIT: Other commenters have confirmed that it is the "motion_type" that causes it, similar to the (now fixed) AD Kain and Lila chaining problem. This is because Kurasame's motion type is his quite lengthy auto attack animation whereas Amelia's Disorder and Prompto's Ballistic use a quick orb casting animation as their motion type.

Completely unrelated flex: Is this a 1frame tolerance?