XPS 15 9570 slow boot and BIOS freezes

My XPS 15 9570 shows the following symptoms: booting is extremely slow and, if I access the UEFI BIOS, I experience freezes lasting 15/20 seconds followed by 3/4 seconds of responsiveness. In addition, booting my Linux installation, even the GRUB menu freezes with the same timing pattern. Finally, I managed to boot Linux from a USB stick; the process took a very long time but, after that, the laptop seems to work more or less fine, no freezes present. When booting from my internal SSD, I can boot Linux only in text mode and, as discussed, booting it is extremely slow. Running the diagnostic software generates freezes as well.

Since I have issues even running the UEFI firmware, I suspect a hardware issue. Does anyone have suggestions on what could be the cause or suggestions on tests to perform? I have already tried unplugging the following:

• SSD
• One RAM bank at a time
• Touchpad
• Wifi card
• Battery
• Fingerprint sensor

I have also cleaned the fans and repasted the processor. After each one of these, I have tried going into the UEFI BIOS and the freezing was still happening.

See also: https://www.reddit.com/r/Dell/comments/sviebl/xps15_9570_bios_freezes_and_computer_slowly_dying/