I have similar problems, due to interference in FM towers.
Is this your case ?
Try this test out. I just had this. My tech was not able to fix this customer. I went to the customers location. I found signal -80/-80 at 4 miles away. I moved the same radio from the roof in the yard. I got -59/-60 signal. I ended up finding that they did remodeling in the house. Every time they turned the light on. It would make the signal go down. What is happening is they have a short in the wire that is creating a 50ft emf field around the garage. Have the customer put the radio on the pole and they work now.
I have done some testing, and it seems to be SNMP packets making them freeze.
SNMP syslogs and traps, going through management VLAN, these are sent as ethernet broadcast.
Some times when a lot of devices reports errors at the same time, these SNMP broadcasts reach 5000PPS.
And this seems to make a lot of the Mikrotik equipment freeze up.
Superdust, please send supout.rif file from this router to support@mikrotik.com
I have a similar problem. I have two RB433’s on the same tower with an ethernet cable running down to a switch linking them together. I also have an ubiquiti airgrid unit on the same tower. When I ping the airgrid from rb433 nr1 it pings fine but when I ping the airgrid or rb433 nr1 from rb433 nr2 then every 50 packets or so I get 3/4 packets lost. I have replaced the network cable as well as tried the other ethernet ports on the routerboard and switch but the problem remains. Tomorrow we will replace the routerboard completely and see what happens.
If your test don’t work,learn and buy a emf tester. Its cheap and will teach you so much. Or just buy shielded cable and make sure you ground the cable.
What is an “emf” tester?
Question about cables. Up to now I only use non-shielded cables. Partially because my supplier also tells me when you you shielded everything in the line, including boards etc. has to be grounded properly to good ground. If not the use of shielded cable is actually worse then non-shielded.
Since good grounding is a problem in the very dry climate I work I am a bit reluctant in use it.
What is your opinion?
Also, off course in shielded cable you need to use shielded RJ-45 connectors. They then connect to the ground of a routerboard when attached to its port?
I have had two occasion where board was not grounded and by fitting a shielded cable the connector actually ´burned´ its self to the port! It looked like a shortcut to me, which I can’t understand how it happened?
When I measure with a multimeter, I measure the -12 (or -18/-24) of the adapter/battery power on the metal outside of the RJ-45 port by using powerfeed by the jack input.
If I use non-shielded PoE power through the PoE port I don’t measure any power on the metal of the port?
If the ground of the jack connects to the ground of the board connects to the metal of the port, why is this not the case when I use PoE without shield?
Any insights in this?
Hi ,
Man i face these problem before all what i do was to remove the full duplex check from interface ether1 Ethernet .
Good luck
Replaced the routerboard but still the same problem. 
Will install shielded cables with grounding next and let you know what happens.
EMF is electromagnetic fields which is caused by electrical cabling. Basically it creates a magnetic field around the cables and this might cause problems on the data cables. Shielded cables are supposed to help against this problem
you must ground the shielded cable or it does nothing.
Rudy, don’t connect nothing to ground.
If you uses shielded cable. Its does not shield unless it is grounded. You can use shielded rj45 ends. Then if you poe supports grounding, it will shield.
But… If you don’t have a good ground, then you’ll have more problems.
I all that really true?
I agree that shielded cables has to be grounded, otherwise they don’t work as being a Gigabit cable (Cat6)
But to keep emf out the shield by itself only should be doing something… Maybe not the best but better than nothing?
The shield act as a ´cage of faraday` and such cage also functions without grounding… proof is a car that is a perfect shield against electricity (lightning strike!) and inside a container on a trailer your mobile phone or wifi device has almost no more receipt of any signal… in both instances perfect insulation from the earth!
So although your statement is right in the first wordings the last two words are not completely true imho.
Reason to start this discussion:
I use many CPE’s with plastic housing, some suggested to use shielded utp cable to bring the earth inside the clients house where the shield could be connected to any part of the house earth grid.
But many houses in my region are very poor earthed themselves and some are all wood! Earthing consists out of a earth network connected to a simple copper rod driven 15cm (!) into the powder dry soil!
Would it now makes no sense at all to earth CPE’s, cables etc? or is some shielding better than nothing? Or maybe it is even worse in this case!
(One electrician keeps telling me that the use of shielded UTP cable while not properly grounded is actually worse than using normal unshielded cable…9
That’s fine. I suppose that’s also true in certain situations. I use emf testers so I know that shielding will or will not fix the issue. Thanks for your input.
Woohoo! Found the problem, but it was not the routerboard and not the shielded cabling. We have two rb433 and two ubnt airgrid m5’s on this site. For some reason I can not understand, the ubnt’s was causing the packet loss. After disconnecting the ubnt’s from the network the packet loss was gone. 
Very strange but at least I found the problem. Thanks for all the help guys!
Yep 2 of my friends had this issue. How I made this work is make sure every ubnt unit has a mikrotik on each side of the ubnt unit and that your in routing mode. Also make SURE that the ubnt is in STP mode.
Dallas
missed this post of yours…
we talk about utp cable here wasn’t it? Anyway, I have been told the same. Better no ground than poor ground for Gigabit cables.
But what is ´good´ ground and what is not? Even some houses in same are very poor grounded. And any installation (tower, mast) on a shed or just on the dry soil has poor ground isn’t it?
In my country of birth soils are almost always wet and the groundwater level is never far. But here in Spain?
Thanks a Million, I enabled stp on the ubnt and now the packet loss is gone! 
Do you ground at both ends or only to the top ? (or to the bottom?)