AC:Valhalla is experiencing severe performance degradation, possibly caused by volumetric effects stacking and not de-rendering, specifically fire and smoke and fog. Over the course of 20 to 40 minutes (depending on how many cutscenes the player goes through) Performance will go from >71 FPS to <30FPS
Performance also degrades when entering very large caves with volumetric effects obscuring their entrance. When using Odin Sight, and when loading back to Eivor after traveling very far away from Eivor as Synin.

There is one temporary fix, reloading the world either from a save game or via relaunching the client. However degradation of performance will return within the 20 - 40 minute time frame, again depending on how many conversations and cinematics the player goes through in that time.

This is repeatable exactly as described on this system.

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System Information
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     Time of this report: 11/30/2020, 13:48:12
            Machine name: VIRUS
        Operating System: Windows 10 Pro 64-bit (10.0, Build 19042) (19041.vb_release.191206-1406)
                Language: English (Regional Setting: English)
     System Manufacturer: Micro-Star International Co., Ltd.
            System Model: MS-7C91
                    BIOS: Default System BIOS (type: BIOS)
               Processor: AMD Ryzen 7 3700X 8-Core Processor             (16 CPUs), ~3.6GHz
                  Memory: 32768MB RAM GSkill TridentZ INTERNATIONAL RGB DDR4 3200 MHz
     Available OS Memory: 32694MB RAM
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Display Devices
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          Card name: AMD Radeon RX 5700 XT
       Manufacturer: Advanced Micro Devices, Inc.
          Chip type: AMD Radeon Graphics Processor (0x731F)
           DAC type: Internal DAC(400MHz)
        Device Type: Full Device (POST)
         Device Key: Enum\PCI\VEN_1002&DEV_731F&SUBSYS_2398148C&REV_C1
      Device Status: 0180200A [DN_DRIVER_LOADED|DN_STARTED|DN_DISABLEABLE|DN_NT_ENUMERATOR|DN_NT_DRIVER]
 Device Problem Code: No Problem
 Driver Problem Code: Unknown
     Display Memory: 24499 MB
   Dedicated Memory: 8152 MB
      Shared Memory: 16347 MB
       Current Mode: 2560 x 1440 (32 bit) (165Hz)
        HDR Support: Supported
   Display Topology: Internal
       Monitor Name: Generic PnP Monitor
      Monitor Model: MSI MAG272QR
         Monitor Id: MSI3CA8
        Native Mode: 2560 x 1440(p) (59.951Hz)
        Output Type: Displayport External
Monitor Capabilities: HDR Supported (BT2020RGB BT2020YCC Eotf2084Supported )
Display Pixel Format: DISPLAYCONFIG_PIXELFORMAT_32BPP
     Advanced Color: AdvancedColorSupported