Of my 250 full MT units (rb + radio) and all running v5.4 with updated firmware and all in simple routing with src-natting on the CPE to separate client LAN form wlan network, I still have roughly 8% of units that have the ethernet ports disabling and enabling.
It happens on almost all type of rb's I have. It happens on equally configured similar hardware units.
Some units it happens only once or twice a day, some units several times an hour!

The strange thing is, clients don't seem to notice them! Most of my client use Skype but I haven't had a single complaint in the last weeks, while my logs are filling with Ethernet disconnects.....

The problem in troubleshooting is that I can't predict when it happens. It is also hard to test since usually it is client's PC or router attached to the port. Meaning I first have to filter disconnects because client disconnects his PC/Laptop/router, secondly I have to filter possible bad connectors out.
I have the ´feeling´that the moment traffic runs over the port, it doesn't happen.
Some units that show the port flap, if I set a ping over it, the issue doesn't happen....
Even the unit that shows many flaps an hour, I log-in wireless (so the wlan port) and the Ethernet port doesn't disable any more!
Sometimes I see an Ethernet port according the log disable, re-enable itself but on lower speed and simplex only, to disable again and immediately enable itself again with the high speed duplex.

So, are the Ethernet ports really disconnecting? Or is it only a faulty messaging system in the ros5.x?

Currently we are unable to reproduce this problem. Anyone else having similar problem, please, send suppout.rif file to support@mikrotik.com.

Anybody already have a solution / workaround for this?
I have now some 15% of all my routers running 5.4 with the port flap issue. But clients don't seem to notice.
The strange thing is only all my routers which have ethernet connections under my control (fixed, no touch etc) don't seem to have the problem.
It only happens to ethernet ports that are connected to either client PC's or client domestic routers....

we have RB1100's with the same problem - ports that flap are connected to another RB1100 and to some Grooves

we have RB1100's with the same problem - ports that flap are connected to another RB1100 and to some Grooves

No, with me its the other way round. Ports connected to other rb's have no issues. It only on ports connected to 3rd party stuff (routers, switches, Pc's)