you can check if your ET1 is disabling WiFi when in standby and then use Zebra RxLogger to collect some data on what is happening on the device.
Here's a guide on how to use RxLogger from last year AppForum:
BTW: which OS build number are you running on your ET1?
The OS build number is 4.1.1 version
Bootloader version 1.1.4(2015 -Mar-2)
I will try to do what you said an i will upload the result
Were you able to identify what was causing the issue. I'm having a similair problem with the et1 when it comes out of sleep. I have to restart the device in order to join the wifi. Any ideas?