Help! My 4th SSD Slot Isn't Recognizing My Drive

I've recently encountered a strange issue with my motherboard and storage setup. I have three SSDs installed: one in the M_1 slot, one in the M_2 slot, and another in the M_4 slot (I had to skip the M_3 slot due to space constraints with a heatsink). However, the SSD in the 4th slot just isn't showing up anywhere—it doesn't register in the BIOS, disk management, device management, file manager, or even in Samsung Magician. It's as if that slot doesn't exist. When I test the SSDs in other slots, they work perfectly fine, but the 4th slot won't recognize anything. The option to move an SSD to the 3rd slot is available, but I'd prefer not to remove the heatsink and risk voiding the warranty. I haven't updated my motherboard or BIOS yet (I'm not home), but before I do, I want to gather other potential solutions for this frustrating issue. I built this computer about a year ago, and my motherboard is an MSI x670e Tomahawk with Samsung 990 Pro SSDs.