Edit 2: 1.6 has a degrading issue. I have 7 pawns in the new save, and the FPS has dropped to 50-70. This is not normal for my pc. :(

Edit: After some testing, I have concluded that something has gone seriously wrong with the initial save I was playing. It is permanently in a state where FPS will simply never recover, and the cause is unknown. New save files appear to be fine. I'm still unable to start the Gravship Scenario, but I don't know which mod is responsible for that.

I have removed the following mods as I was not using them much anyway, and I'll see what happens when I wake up.

Holsters
All 5 Music Expanded Mods
Vanilla Achievements Expanded
Vanilla Apparel Expanded - Accessories
Vanilla Fishing & Treasure
Vanilla Plants & More Plants
Vanilla Weapons Coilguns, Non-Lethal, Quickdraw and Tribal

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Original post:

So, this wasn't happening with 1.5. Before, I was getting 120+ Fps on normal speed, and now it's swinging between 20 and 90 on normal speed. Sure, I have quite a few mods, but I've also lost quite a few mods due to the fact they have not updated. I also have an odd quirk of not being able to start the new Gravship scenario. The map spawns, but no ship, no pawns, nothing.

The following is my current mod list. No, I do not use a mod to sort it. Those marked (outdated) are still working, at least to the point of not causing any errors in the boot up logs. Any help is appreciated in alleviating the FPS tanking and/or load order.

Harmony
Core
Royalty
Ideology
Biotech
Odyssey
[FSF] Filth vanishes with rain and time
Adaptive Storage Framework
Cherry Picker
Vanilla Expanded Framework
Alpha Biomes
[FSF] Simply Soil
AI Upscaled Textures - Core
Vanilla Achievements Expanded
Vanilla Weapons Expanded
Vanilla Weapons Expanded - Grenades
Reel's Expanded Storage
[SYR] Processor Framework
Vanilla Textures Expanded
Vanilla Outposts Expanded
Vanilla Furniture Expanded - Architect Module
Vanilla Psycasts Expanded
Alpha Animals
Alpha Genes
Animal Controls
Animals Logic
Beautiful Outdoors
Better Explosions
Bionic Icons
Blueprints
HugsLib
Character Editor
Vanilla Plants Expanded
Clean Textures
Common Sense
Compact Hediffs
DragSelect
Drop Loot When Destroyed Framework
Dubs Break Mod
Enemy Self Preservation (outdated)
Vanilla Pawns Retextured
Erin's Body Retexture
Erin's Cottage Collection
Expedient: Wastepack Solution (outdated)
Fahrenheit and Celsius
Fix Mechanoid Resource Drop (outdated)
Food Poisoning Stack Fix (Continued)
Harvest Everything! (outdated)
Holsters
Don't Block Door (outdated)
Just Ignore Me Passing (outdated)
Just Put It Over There
MineItAll - unofficial (outdated)
MinifyEverything
More Vanilla Textures
Muzzle Flash
No Burn Metal
Optimization: Meats - C# Edition
RandomPlus
Realistic Rooms Rewritten
Vanilla Furniture Expanded
RimHUD
Seasonal Weather (Continued)
Smart Speed
Smarter Construction
Pick Up And Haul
Stack XXL
Stonecutting Extended
Tainted Renaming
Tilled Soil
TradeHelper
Ugh You Got Me
Utility Columns
Vanilla Animals Expanded
Vanilla Apparel Expanded
Vanilla Armour Expanded
Vanilla Books Expanded
Vanilla Brewing Expanded
Vanilla Cooking Expanded
Vanilla Cooking Expanded - Stews
Vanilla Events Expanded
Vanilla Factions Expanded - Classical
Vanilla Fishing Expanded
Vanilla Fishing Expanded - Fishing Treasures Addon
Humanoid Alien Races
Alpha Bees
Vanilla Genetics Expanded
Vanilla Hair Expanded
Vanilla Hair Retextured
Vanilla Plants Expanded - More Plants
Vanilla Skills Expanded
Vanilla Furniture Expanded - Power
Vanilla Furniture Expanded - Production
Vanilla Furniture Expanded - Prop and Decor
Vanilla Textures Expanded - Variations
Vanilla Weapons Expanded - Coilguns
Vanilla Weapons Expanded - Heavy Weapons
Vanilla Weapons Expanded - Non-Lethal
Vanilla Weapons Expanded - Quickdraw
Vanilla Weapons Expanded - Tribal
Various Spaceship Chunk (Continued)
We Are United
WeaponStats
What's That Mod
Doormats
Dynamic Diplomacy - Continued
Plasteel Surgery (Continued)
Romance On The Rim
Vanilla Social Interactions Expanded
Metabolic Adjusters V2
Better Gene Inheritance
Self Dyeing
Positive Connections
RimCities
Ice Blocks
Crafting Quality Rebalanced
QualityBuilder
Vanilla Furniture Expanded - Spacer Module
Vanilla Furniture Expanded - Medical Module
Travel through water (outdated)
Child Apparel (outdated)
Moonlight Greatswords
Orphanage and Daycare
Stone Conversion Recipes
[ARY] Automatic Stump Chopping [1.5 - 1.6]
Thrumbo Plushie
Vanilla Apparel Expanded - Accessories
Vanilla Ideology Expanded - Memes and Structures
Combat Readiness Check (Continued)
Vanilla Psycasts Expanded - Hemosage
Gemstones
Vehicle Framework
Pioneer Rock
Colorable Sheep (outdated)
[HRK] Medieval deathrest coffin
Hospitality
Hospitality: Casino
Cash Register
Hospitality: Storefront
Hospitality: Vending Machines
[KV] Save Storage, Outfit, Crafting, Drug, & Operation Settings [1.5/1.6]
Scavenging
Opulent Gold (outdated)
No ZzZ
No Hemogen Farm Medical Alert
Neutroamine craftable
Music Expanded Framework (Continued)
Music Expanded: Elder Scrolls
Luciferium craftable
Bad Can Be Good (Continued)
ApplyPressure
[GTG] Massive Cargo Trader
Music Expanded: Baldur's Gate 3
Children Learn on Caravan
Memorial Stele
Erin's Hairstyles 2
Mines
Fog Color Changer
More Ritual Rewards
Upscaled - Won hair_men
Upscaled - Won hair_women
Float Sub-Menus
Categorized Bill Dropdown
Searchable Menus
Expanded Floors
Glitterstone
More Animal Beds (outdated)
Geothermal Power Extenders (outdated)
[sbz] Vanilla Stuff Colors
I Clearly Have Enough! (Continued)
Simple more slaves
What's for sale?
Alpha Books
Music Expanded: Halo Franchise
Music Expanded: Fallout
MendAndRecycle
All Stones Are the Same
LWM's Adaptive Deep Storage
Visitor Spot
Wider Marriage Spot
Quality Colors (1.6 Temp)
Designator Shapes
Bleu's Horse Recolors
Go the Fork to Sleep
Learning Desk
Meatleaf
Quarry (1.6 Temp)
Vanilla Vehicles Expanded
Where's Center?
Dragons Descent
DragonBond
Search and Destroy (Continued)