I'm completely new to coding, reading and understanding but I think it might be a SMAPI error? If not, could you point me in the right direction.

Here's the log:

[10:04:18 ERROR SMAPI] An error occured in the base update loop: System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at StardewValley.Debris..ctor(Int32 objectIndex, Vector2 debrisOrigin, Vector2 playerPosition)
at StardewValley.GameLocation.monsterDrop(Monster monster, Int32 x, Int32 y)
at StardewValley.Locations.MineShaft.monsterDrop(Monster monster, Int32 x, Int32 y)
at StardewValley.GameLocation.damageMonster(Rectangle areaOfEffect, Int32 minDamage, Int32 maxDamage, Boolean isBomb, Single knockBackModifier, Int32 addedPrecision, Single critChance, Single critMultiplier, Boolean triggerMonsterInvincibleTimer, Farmer who)
at StardewValley.Tools.MeleeWeapon.DoDamage(GameLocation location, Int32 x, Int32 y, Int32 facingDirection, Int32 power, Farmer who)
at StardewValley.Farmer.showSwordSwipe(Farmer who)
at StardewValley.FarmerSprite.currentAnimationTick()
at StardewValley.FarmerSprite.animateOnce(GameTime time)
at StardewValley.FarmerSprite.checkForSingleAnimation(GameTime time)
at StardewValley.Farmer.Update(GameTime time, GameLocation location)
at StardewValley.Game1.UpdateCharacters(GameTime time)
at StardewValley.Game1.Update(GameTime gameTime)
at StardewModdingAPI.Inheritance.SGame.Update(GameTime gameTime) in D:\source_Stardew\SMAPI\src\StardewModdingAPI\Inheritance\SGame.cs:line 338

Hi @Bremusa. That problem is usually caused by outdated XNB mods or corrupted game files. Try verifying the game integrity to fix that. Note that any XNB mods will be removed (but SMAPI mods won't be affected).

If you need more help, come talk on Discord or in the forums. :)