PC became slow after case swap and AIO install

A few days ago I moved my build into a new case (Lian Li Lancool 207) and replaced my air cooler with an Arctic Liquid Freezer III Pro 360 A-RGB. I did not change any other hardware.

Since then, the PC has been behaving strangely and is much slower overall. Programs take much longer to open, some games suddenly take forever to load, and in one case a game that used to load in about 15 seconds got stuck indefinitely on the loading screen. For the first 2 days the PC was so slow that it was basically unusable. Since then it has improved somewhat, but it is still noticeably slower than before and many things still take much longer to load.

What I already checked:

• CPU temps are normal in HWiNFO64
  • around 40°C idle
  • around 55°C in games
• No obvious throttling
• DOCP is enabled (same as before)
• BIOS settings are the same as before
• GPU-Z shows PCIe 4.0 x16 @ x16 4.0
• I ran 3DMark Time Spy and the score is a bit lower than expected, but still in a normal range:
  • Overall: 16,944
  • Graphics: 19,035
  • CPU: 10,444
• I also ran CrystalDiskMark on my SSD and the results looked normal

Specs:

• Ryzen 7 5700X
• ASUS Radeon RX 7800 XT Dual OC
• ASUS Prime B550M-A WiFi II
• 32 GB G.Skill Aegis DDR4-3200 CL16
• Verbatim Vi3000 2 TB
• Seasonic G12 GM 750W
• Windows 11

At this point I’m not sure whether this is:

• a Windows/driver issue caused by the hardware swap
• some kind of cooler mounting or thermal paste issue even though temps look fine
• another hardware issue
• or something else entirely

Does this sound familiar to anyone, and what would you check or try next?