Air carrier First Officer reported during cruise flight the aircraft began to depressurize. Various cargo ECIAS messages appeared causing a divert to a nearby airport.

Narrative

I was the relief pilot for flight and had returned to the cockpit around XA00 from the first break where I took the position of pilot flying. Near XA15 during conversation with the captain; I mentioned feeling pressure changes in my ears and noticed the pressure gauge showed the cabin descending at a rate of around 300 feet per minute while we were still mostly maintaining a cabin altitude of ~8000 ft. I thought this could just be an indication error in the analog gauge. However about 15 minutes later we received several EICAS caution alerts in rapid succession. Within a few seconds I saw alerts for the aft bulk cargo door; forward cargo door and emergency doors not being properly secured. Then there were a series of aural alerts and several more EICAS cautions changing and happening too quickly to remember. My immediate thought was that a rapid decompression was imminent and wanted to descend - so we asked the flight attendants to take their jumpseats. It was unclear which checklist to run given the multiple cautions but I decided on the emergency doors checklist since that was the alert that I noticed for the longest time; while the captain referenced the aft bulk cargo checklist. We were at the same time observing pressure bumps and quick changes in the pressure gauges. Both decision trees led us to descending to 14;000 ft and a similar resolution so we asked for and received vectors from ZZZZ control for the descent and [requested priority handling]. At some point during the descent the caution messages disappeared and didn't return for the remainder of the flight. In consultation with dispatch we decided to divert to ZZZZ [airport]; had the 3rd pilot return to the right seat and briefed the flight attendants on the plan. We completed the abnormal checklist items and the remainder of the flight and approach was uneventful. After landing the flight attendants in the aft galley informed us that door 2L was extremely loud during the approach.