1. Did you update firmware after installing the RMM4?
2. Switch the two RMM4's on your systems and see if the issue sticks with the RMM4. If yes get it replaced.
Yes, i update the firmware after installing the RMM4. It's actually very weird. After unplugging all the cables in that VLAN from the switch and plugging them back in everything returned to normal. The packet drops appear after recovering from AC power failure. Sometimes it comes back to normal, sometimes it has packet drops. After a few tries even the first one began to have problems. Now everything returned to normal. I'll keep testing it for a few weeks and see what happends. i'm starting to belive it's not the modules.
I must also mention that i don't have an Intel chassis, i have a normal desktop case, a CoolerMaster with a Sirtec HighPower 500W power supply. The systems are used for testing in a home lab so no production environment.