B5c radio : traffic movements stop in day time, works during night time

HI there,
I have a backtoback PTP link connected as follows:
[Mikrotik---->B5c----->B5c(lan-to-lan connected)B5c-----> B5c—>Mikrotik]

Wireless link seems fine and throughput is symmetric over the whole segment.
The issue is that it stops traffic flows during the day time, but it works fine in night time.
We have done reboots, checked cabling, checked the L2 part and radio configuration parts as well, Could not find the exact issue for no traffic flow during day time.

Please suggest its solution…

I would watch the links and see where the break happens. Could be any of the pieces of equipment, without knowing more of where the break is and what the equipment is reporting when it breaks there isn’t really much help any of us here can be…

Can you be at one or the other end of the links to do diagnostics? Depending on the config that you are using you should be able to access the whole link and watch what happens.

Since it fails during the day, a couple of other things also come to mind (they’re unlikely, but possible):
Is one of the radios failing as it gets warmer out?
Could there be some business turning something on that interferes with the radio signal? If so, I would expect it to be fairly consistent on the time of day the problem starts and stops.

How many degrees is the air temperature?

air temperature is normal.
its about 2-3 degress C in night time,
about 12-13 deg C in day time.

Yes, whole link is accessible. Link seems fine but traffic movement stops in day time.

If both links are working, but only traffic stops, it sounds a lot as if there’s a time based ACL somewhere in the link. How consistent are the start & stop times?

The main thing I can think of doing is to ping from each end, going 1 device at a time until you find the device you can’t reach. Yes, do this from each end to make sure the problem is the same device in each direction. Then, using your original description,
[Mikrotik---->B5c----->B5c(lan-to-lan connected)B5c-----> B5c—>Mikrotik]
#1.-.-.-.-.-.-.-#2.-.-.-.-.-#3.-.-.-.-.-.-.-.#4?.-.-.-.-.-.-.-#5.-.-.-.-.-.#6.-.-.-.-.-.#7
let us know where the pings fail in each direction. I’ve added numbers to simplify the discussion. How many devices are located at #4?

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13°C is approximately 55°F. However, just because the temperature is not excessive does not mean that a bad component may be working at the cooler temperature and failing at the warmer temperature. It doesn’t have to be overheating if the component is bad. However, with the temperatures you have listed, that’s probably one of the last things to look at.