I’ve had a couple of games recently were it was me as Torvald trying to damage an (Elder) Kraken.
What I noticed is, that more often that I would like, the Mortars seem to explode very close to the Monster but the Healthbar shows no white burst damage. I have taken a look at the stats provided by @white_hawke8 (which means typos can not be excluded entirely) and it looks like I have found the problem.
Torvald’s Mortar Cannon
4 meter minimum explosion radius
8 meter maximum explosion radius
Detonates within 10 meters of monster
The proximity detonation is at 10 meters but the outer radius only at 8. So it is entirely possible that a Mortar detects the Monster but the explosion radius is 2 meters too short.