Thank you all for the suggestions. The issue appears to be resolved, although I am not sure what did it, so I'll just detail my steps here:

• I check in the BIOS the voltage of both 5v and 12v rails, they were well within error margins.
• Since most answers suggested something in relation to power supply, I disconnected and reconnected all cables plugged into the PSU, as well as moved the front I/O cable further from PSU cables. It was tangled in one of them and I feared some sort of interference.
• I also disconnected and reconnected the front I/O USB cable.

After all that, the issue seems to be resolved.

Thank you all for the suggestions. The issue appears to be resolved, although I am not sure what did it, so I'll just detail my steps here:

• I checked in the BIOS the voltage of both 5v and 12v rails, they were well within error margins.
• Since most answers suggested something in relation to power supply, I disconnected and reconnected all cables plugged into the PSU, as well as moved the front I/O cable further from PSU cables. It was tangled in one of them and I feared some sort of interference.
• I also disconnected and reconnected the front I/O USB cable.

After all that, the issue seems to be resolved.