Dropping Connection with internet

I would like to ask for some inquiries about the problem that we are experiencing now.

currently we have 6 EPMP1000 cambium radios connected on 4 sites. from the 1st year, we have been smoothly connected the sites with 1 single ISP. unfortunately, comes last month that we have experienced intermittent connection for the 2 remote site. this is at the least 1-2KM away from each other. our vendor visited us to check on this problem where we found out that if the ISP is not connected, clean traffic that has 0 RTO but whenever we connect the ISP, comes the intermittent where after a minute it disconnects and reconnects after 30 - 1 minute seconds. affected is just the 2 remote offices.

Here is the link between offices

Site 1 - Antenna 1

Site 2 - Antenna 2 - 3

Site 3 - Antenna 4 - 5

Site 4 - Antenna 6

This is just a representation of the simulation/troubleshooting that we performed:

                     With ISP          Without ISP

Antenna 1     Connected      Connected

Antenna 2     Connected       Connected

Antenna 3     Connected      Connected

Antenna 4     Intermittent      Connected

Antenna 5     Intermittent      Connected

Antenna 6     Intermittent      Connected

So, I am assuming, antenna 1 at site 1 is master to antenna 2 at site 2....antenna 3 at site 2 is master to antenna 4 at site 3, and antenna 5 at site 3 is master to antenna 6 at site 4? Something like this?; 1 <------>2-3 <----->4-5 <----->6

And when you say disconnects, do you mean the actuall wireless connection between "antennas" drops or does data flow just cease? It seems from your flow chart that either data flow from 3 to 4 stops or the link drops, which of course either scenario will kill any data flow down the line. Can you advise which it is, data ceases or link drop? Can you also advise what equipment is in the ethernet chain from antenna 3 to antenna 4? 

You may want to post your syslog file for antennas 3 and 4 from when link dies as well (Monitor > System Log).