Solution to your problem, maybe:
Your main issue is the idea of Loads and how abstract they are for combat. I personally have never minded the idea of Loads for Throwing knives and arrows, but if you want to get right in there and say that a Volley is a about a third of the maximum arrows they can carry within that quiver, that should work just fine.
I would advise that you at least try the Load bit, to see how it flows with your players. It maybe annoying, or weird, but its always worth trying something new. Since you’re an experienced GM, trying something new probably won’t be too tough on you. If they kick up a fuss, next session just change it around.
The Idea of losing arrows during combat due to Volley and Load is mostly to be interpreted by what the player is doing
Arrows are meant to be kept in bundles, so when you do a Load or Volley, you take the whole bundle out, set it in front of you, and just shart speed-shooting like it’s the end of the world.
For complications, maybe while volleying you shot a few too many in an attempt to cover more ground. Maybe you are frantic in grabbing your arrows and drop a few. Maybe you think you’re Legolas and load like 5 at a time or something.
A complication is usually a small incident that can be solved by a single action, so dropping your arrows on the floor and forcing you to pick them up to fire seems pretty reasonable. If the GM spends some doom, they may be a little meaner - might make it that the quiver strap is loose and it all falls over a crevice, or that a rat eat them or something. I don’t know, make something cool up.
Always make the complications and the doom spend match the story - maybe you did climb that rock with like 1 arrow because you were in a hurry to get to a good posistion. Maybe you are caught unawares and grab your quiver while jumping out of a window to avoid cultists trying to take your tongue. Maybe you hit the ground hard when you fell off the crevace and your arrows broke your fall. Maybe you can’t spell Position. Whatever matches what you are doing, make the complication and the fiction match for that.