MikroTik CRS310 and U7 Pro Max - auto negotiation issues

Hi All,

I have a weird issue with a CRS310-8G+2S+IN.

A few words first about the setup. In my room I have a UniFi U7 Pro Max connected to my CRS310-8G+2S+IN. The AP is powered on via a UniFi PoE injector and has a 2.5Gb interface. I also have the exact same setup (U7 Pro Max connected to a CRS310 via PoE injector) in my living room.

Now, a few words about the problem.

At my room's setup everything works fine for a couple of days and both UniFi's controller and my CRS310 report that the AP is rated at 2.5Gbps Full Duplex. After a couple of hours/days and for no apparent reason, the Rate will fall to 100Mbps (Fast Ethernet) until the AP will lose connectivity (I cannot even ping it).

On the other hand, the same setup in my living room is rock solid for months.

At first I though it was the cables' (CAT6a) fault, so I replaced them. Nothing changed. I also replaced the PoE injector, but again, no changes. Then I though that the U7 in my room might just be faulty, so I moved the AP that I had in my living room (and was fully stable for months) to my room. To my surprise, after a few days I had the exact same issue. Even the second AP was losing connectivity. I then started thinking that the port on my CRS310 was the one causing the problem so I switched ports. And once again, I saw my U7 appearing as offline...

I've also tried disabling auto negotiation and manually setting advertisement to 2.5G, but this also had no effect since the problem re-appeared after a while.

I've started thinking that the problem is the MikroTik CRS310 that I have in my room, since I've tried everything I can think of without solving the problem, while the second CRS310 is rock solid.

Has anyone seen this issue before?