Strange behavior between my nodes and gateway

Hello All,
I have a strange behavior and I would like to know if you can help to understand.

Let me first describe how is my structure.

I have 2 nodes in a orchard at about 450m altitude. There are not above the tree and the foliage, but on the top (you we will better understand later). One of station is in the middle of the orchard and the second at the end.

The gateway it on the top of my camping car, at about 900m of the first station and about 1100m of the second.

I know that my gateway is not well located because it is at a lower altitude than my nodes and there are win-yard between them.

Between June and September 2018, in general the transmission were fine.

End of April 2019, I turned on my nodes and the gateway for new measurements, while the trees did not have foliage yet and the transmission started well (the nodes transmit each hour). The leafs appeared and grew up. And suddenly, at the same time (within one hour) , the node could not transmit to the gateay

As it happen at the same time, I though about a problem with the gateway, but not. Then I moved the gateway at about 500m from the nodes, almost at the same altitude and the area is clearer. The nodes stated to transmit again. Great!

It ran well for about 2 weeks until my Gateay MicroCard broke. I changed and reinstalled it. The nodes transmitted again but only fro 4 hours.

Both nodes stop transmitting at the same time again

I thought again an issue with the new installed gateway, but not, the gateway worked perfectly. Then, I moved the gateway at about 50m from the nodes and the nodes started transmitting!

My guess is as the foliage “covers” the nodes (even if there are at the top of the tree), the foliage act as an obstacle, but it can not explain why the two nodes stopped transmitting at the same time, first all because the apple tree has very less foliage at the second node. My guess is the foliage would make an obstacle, the node will not stop transmitting during the same hour, but may be, with a couple of days of delay.

Then I would to understand why this behavior?
Why the node stop transmitting at the same time, and why it works when I move closer the gateway, while last year, it worked at 1km of distance.

Can it be the power of transmitting, how changed automatically?
I configured as in the example: https://github.com/matthijskooijman/arduino-lmic/blob/master/examples/ttn-abp/ttn-abp.ino#L218

Note, I am using for now (but I will change to OTAA) ABP activation method.

Thank for your point of view and have a nice evening/day.
Cheers

I doubt the nodes stopped transmitting (as they do not “connect” to a gateway, but just transmit when they want to, and have no clue if their transmission is received). My guess would be that the gateway’s range (sensitivity) somehow dropped.

How did you test “the gateway worked perfectly”?

Hello

I doubt the nodes stopped transmitting

Yes that’s true. I would say, the gateway do not transmit the message, ot it’s not received.

How did you test “the gateway worked perfectly”

In fact, my statement is not correct as well. I was a bit to much optimist.
The router works well and I could see the gateway with a green light on the TTN console. I could see "connected with the the “last seen” time.

My guess would be that the gateway’s range (sensitivity) somehow dropped.

Ok but how can I check it?