(Help need) 433.92MHz Remote controller strange issue

[BD1QMP]

A small product use standard 433.92MHz Remote controller module from Taobao. The transmitter and receiver is in figure 1
the reverse schematic drawn by myself, in figure 2 and figure3.

More than 100 unite are installed in different sites. the sites room is lead shield.
Normal case: push the transmitter button, the receiver will enable output, when release the button, the receiver will stop output.

Only 2 sites have this issue.
The issue is: push the transmitter button, the receiver will enable output, when release the button, the receiver will stop output. about 200-500ms later, the receiver will enable output again, and after about ~1s (it is random), the receiver stop output.  It is easy to repeat the issue once per 3 times.  I tried to turn off the transmitter power supply, the receiver has the same issue.

I tried 4 units in that site, all the 4 units have same issue. when I take the products back, cannot repeat the issue. 

It is so strange!

Can any one give me some advice for investigation?

Thank you very much!

DE BD1QMP
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[AFTORF]

It's seems to be RFI. Did you check RF field with receiver or spectrum analyzer ?

[BD1QMP]

It's seems to be RFI. Did you check RF field with receiver or spectrum analyzer ?

no，I didnot check it

[AFTORF]

You said "more than 100 units installed" but you don't have any receiver or analyzer to hear or watch RF path between transmitter and receiver...