I have as central rb4011, there are more ptp links going out. One of them is AF5X. I had problems with everything connected to rb4011. Latency on ethernet went up to 100ms. After months of laboring I find problem with af5x ethernet. I connected between af5x and rb4011 switch and this solved the problem partially, latency dont go up and everything works like should, just AF5X is problematic. I read that this is related tu manufactural problem of af5x. UBNT keeping calm about this issue.
So be careful if you connect af5x to some devices and traffic there is over 100mbit/s.
I have had the same problem with these AirFiberX devices too.
The UBNT AF5X have an issue with both their ethernet ports, all socket RJ45 golden pins normally have a slight concave shape so that it sits nicely contacting the RJ45 male plug gold contacts, but in the AF5X AirFiber5X they are bent 180 degrees the wrong way therefore the only place of contact is on the end of the male plug which subsequently wears off the gold and causes bad contact and therefore flapping of the interface. Typically takes about 4 to 6 months to manifest a flapping issue and caused by the wind slightly moving the cable and its plug.
By disabling the Mikrotik ethernet port connected to the AF5X and re-enabling it will create enough of a voltage jump across the contacts to allow ethernet link up again or maybe to go from 100Mb to 1000Mb, but this is only temporary for a day or week. Best option is to solder in a new ethernet socket port, which you can buy from Mouser.com part nr 651-1149882 description Modular Connectors / Ethernet Connectors CUC-SP-J1ST-A/R4LT-SMD and otherwise use option B which is to bend the pins using a pair of mini pliers but here one needs far too much patience for. The new version AF5XHD is correctly designed with the concave pins in the correct direction.
Cheers Daniel Beckmann
WISP Netherlands