Not sure what could be the problem; tried toggling some visual settings but still getting a main engine crash about 10% into the fight. I'm using Calamity weapons and gear in the fight and have several other mods running.
Here's the part of the log that has the errors - any pointers greatly appreciated:

[11:56:22.561] [Main Thread/WARN] [tML]: Silently Caught Exception:
System.Collections.Generic.KeyNotFoundException: Radiance.EmpressProjectileLance
at Radiance.VFX.RadiantWeaponFX.EtherealLanceFX.PreDraw(List`1 projectiles) in Radiance\VFX\RadiantWeaponFX\EtherealLanceFX.cs:line 59
at Radiance.VFX.RadiantWeaponDrawer.DrawBeforeProjectiles() in Radiance\VFX\RadiantWeaponDrawer.cs:line 96
at Radiance.ProjectileTweaks.<>c.<Load>b__11_0(orig_DrawProjectiles orig, Main self) in Radiance\ProjectileTweaks.cs:line 38
at Hook<System.Void Radiance.ProjectileTweaks/<>c::<Load>b__11_0(Terraria.On_Main+orig_DrawProjectiles,Terraria.Main)>(Main )
at SyncProxy<System.Void Terraria.Main:DrawProjectiles()>(Main )
at DMD<System.Void Terraria.Main:DoDraw(Microsoft.Xna.Framework.GameTime)>(Main this, GameTime gameTime)
at SyncProxy<System.Void Terraria.Main:DoDraw(Microsoft.Xna.Framework.GameTime)>(Main , GameTime )
at Terraria.Main.Draw_Inner(GameTime gameTime) in tModLoader\Terraria\Main.cs:line 52843
at Terraria.Main.Draw(GameTime gameTime) in tModLoader\Terraria\Main.cs:line 52830
at Microsoft.Xna.Framework.Game.Tick() in D:\a\tModLoader\tModLoader\FNA\src\Game.cs:line 562
at Microsoft.Xna.Framework.Game.RunLoop() in D:\a\tModLoader\tModLoader\FNA\src\Game.cs:line 878
at Microsoft.Xna.Framework.Game.Run() in D:\a\tModLoader\tModLoader\FNA\src\Game.cs:line 419
at Terraria.Program.RunGame() in tModLoader\Terraria\Program.cs:line 266
at Terraria.Program.LaunchGame_(Boolean isServer) in tModLoader\Terraria\Program.cs:line 240
at Terraria.Program.LaunchGame(String[] args, Boolean monoArgs) in tModLoader\Terraria\Program.cs:line 213
at Terraria.MonoLaunch.Main_End(String[] args) in tModLoader\Terraria\MonoLaunch.cs:line 78
at Terraria.MonoLaunch.<>c__DisplayClass1_0.<Main>b__1() in tModLoader\Terraria\MonoLaunch.cs:line 64
at System.Threading.Thread.StartCallback()

[11:56:22.562] [Main Thread/ERROR] [Terraria]: System.Collections.Generic.KeyNotFoundException: Radiance.EmpressProjectileLance
at Radiance.VFX.RadiantWeaponFX.EtherealLanceFX.PreDraw(List`1 projectiles) in Radiance\VFX\RadiantWeaponFX\EtherealLanceFX.cs:line 59
at Radiance.VFX.RadiantWeaponDrawer.DrawBeforeProjectiles() in Radiance\VFX\RadiantWeaponDrawer.cs:line 96
at Radiance.ProjectileTweaks.<>c.<Load>b__11_0(orig_DrawProjectiles orig, Main self) in Radiance\ProjectileTweaks.cs:line 38
at Hook<System.Void Radiance.ProjectileTweaks/<>c::<Load>b__11_0(Terraria.On_Main+orig_DrawProjectiles,Terraria.Main)>(Main )
at SyncProxy<System.Void Terraria.Main:DrawProjectiles()>(Main )
at DMD<System.Void Terraria.Main:DoDraw(Microsoft.Xna.Framework.GameTime)>(Main this, GameTime gameTime)
at SyncProxy<System.Void Terraria.Main:DoDraw(Microsoft.Xna.Framework.GameTime)>(Main , GameTime )
at Terraria.Main.Draw_Inner(GameTime gameTime) in tModLoader\Terraria\Main.cs:line 52853
at Terraria.Main.Draw(GameTime gameTime) in tModLoader\Terraria\Main.cs:line 52834
[11:56:22.679] [Main Thread/FATAL] [tML]: Main engine crash

System.Collections.Generic.KeyNotFoundException: Radiance.EmpressProjectileLance
at Radiance.VFX.RadiantWeaponFX.EtherealLanceFX.PreDraw(List`1 projectiles) in Radiance\VFX\RadiantWeaponFX\EtherealLanceFX.cs:line 59
at Radiance.VFX.RadiantWeaponDrawer.DrawBeforeProjectiles() in Radiance\VFX\RadiantWeaponDrawer.cs:line 96
at Radiance.ProjectileTweaks.<>c.<Load>b__11_0(orig_DrawProjectiles orig, Main self) in Radiance\ProjectileTweaks.cs:line 38
at Hook<System.Void Radiance.ProjectileTweaks/<>c::<Load>b__11_0(Terraria.On_Main+orig_DrawProjectiles,Terraria.Main)>(Main )
at SyncProxy<System.Void Terraria.Main:DrawProjectiles()>(Main )
at DMD<System.Void Terraria.Main:DoDraw(Microsoft.Xna.Framework.GameTime)>(Main this, GameTime gameTime)
at SyncProxy<System.Void Terraria.Main:DoDraw(Microsoft.Xna.Framework.GameTime)>(Main , GameTime )
at Terraria.Main.Draw_Inner(GameTime gameTime) in tModLoader\Terraria\Main.cs:line 52853
at Terraria.Main.Draw(GameTime gameTime) in tModLoader\Terraria\Main.cs:line 52834
at Microsoft.Xna.Framework.Game.Tick() in D:\a\tModLoader\tModLoader\FNA\src\Game.cs:line 562
at Microsoft.Xna.Framework.Game.RunLoop() in D:\a\tModLoader\tModLoader\FNA\src\Game.cs:line 878
at Microsoft.Xna.Framework.Game.Run() in D:\a\tModLoader\tModLoader\FNA\src\Game.cs:line 419
at Terraria.Program.RunGame() in tModLoader\Terraria\Program.cs:line 266
[11:56:22.680] [Main Thread/DEBUG] [TerrariaSteamClient]: Send: shutdown