Its like that
on rb2011 are connected 10 units (ubnt and mikrotik) after a 1-2 days
rb2011 is freezing its not accessible, units that are connected from 6-10 ports are not accessible also
units connected from 1-5 ports are accessible?
it has happened to me on 3 units, only fix is hard reboot
Try upgrade to 6.1 http://download2.mikrotik.com/routeros/6.1/routeros-mipsbe-6.1.npk
it have fix to this problem
Hmmm…
Recently (actually i’m running the unit for a few months) i’ve started experiencing loss of connection between the left (gigabit switch) port group 1-5 and the CPU. The ports on the 100Mb switch work fine tho.
Phy on machines seems working but no way to access the RB from those ports.
I got the gigabit ports in switch mode (one master, rest are slaves).
Reboot helps OR just disable/enable of the master port.
Not sure why this happens.
v6.1 looking promising till now no problem of that kind
I have had this happen on 6 RB2011 now. It freezes up; bridges all the ports [or acts that way] and the only fix is a reboot. Everything can talk through it but not to it; and no mac-telnet or IP access; it is like it does not even exist; just acts like a dumb switch. I thought it was just on 5.21; but then I had it happen on 5.25 today. Anyone that denies that this is happening is lying 
.
The changelog for 6.1 says nothing about this. We will need to escalate to Mikrotik. This is a real problem.
yes there is noting in change log about that problem
it seem its fixed in 6.1 try it.