The game throws a division by zero exception on line 128 of SalvagingMenu.java in getSalvageCounts when placing some items in the salvaging table. It appears stack.getMaxDamage() has the possibility of being 0 on some items even if they're damageable (don't ask me how!).
I had this happen with Epic Knights' face helmet, which is a seemingly bugged item, but it seems to be an easy fix to add to the salvaging menu anyway.

latest.log

This is... technically an issue with the other mod. I can do something to not crash, but I'll be adding a warning message that blames the offending mod for returning zero here.

Do you get a similar error when you do the following?

1. Run /give @s diamond_pickaxe[max_damage=0]
2. Reforge the diamond pickaxe.
3. Place the reforged pickaxe in the salvaging table.

Similarly, does the server divide by zero when you reforge the bugged helmet then place it in a hopper facing the salvaging table?

Also, can you please try running /data get entity @s SelectedItem while holding the bugged helmet and post the output here?

1. you can't set a minecraft:max_damage component of 0 in a command, it must be a positive number. Using /data modify entity @e[type=item,sort=nearest,limit=1] Item.components set value {"minecraft:max_damage": 0} on the pickaxe to set the component to 0 will also discard the component from the item entirely - using a positive value works as expected
2. yes
3. pretty printed for legibility

{
	components: {
		"apotheosis:rarity": "apotheosis:mythic",
		"apotheosis:durability_bonus": 0.61421025f,
		"apotheosis:sockets": 1,
		"apotheosis:affix_name": {
			with: [
				{
					translate: "affix.apotheosis:armor/attribute/ironforged"
				},
				{
					"": ""
				},
				{
					translate: "affix.apotheosis:armor/attribute/blessed.suffix"
				}
			],
			color: "#ED7014",
			translate: "misc.apotheosis.affix_name.three"
		},
		"apotheosis:affixes": {
			"apotheosis:armor/dmg_reduction/grounded": 0.48466235f,
			"apotheosis:armor/dmg_reduction/deflective": 0.9633712f,
			"apotheosis:armor/dmg_reduction/runed": 0.16254216f,
			"apotheosis:armor/attribute/fireproof": 0.9293304f,
			"apotheosis:generic/attribute/lucky": 0.99269307f,
			"apotheosis:armor/attribute/ironforged": 0.632133f,
			"apotheosis:armor/attribute/blessed": 0.73562926f
		}
	},
	count: 1,
	id: "magistuarmory:face_helmet"
}

The mod seems to set the durability of the armor slots for its armor definition to 0 by default
and certain slots are then configured

Maybe these other slots aren't meant to be obtainable / don't have an item or sth.
In which case they might have put the durability for this helmet you're having a problem with in the wrong durability-array-index