ATO/AWC Level Control Malfunction - Profilux 4

[otimer]

Hello,
I have been running a Profilux 4 since Jan 2019 (20 months). It has been OK allways so far.
I'm so satified with the reliability and the functions.
My AWC is initiated at 21:00 every day and ATO is set allways active. Last evening, I heard some gargling sound in the sump.
And I found tht the AWC drain pump did not stop at Level Sensor 2. I completed manually filling it up to the Level Sensor 1.
This afternoon I observed the water level is far below Level Sensor 1, which means ATO has not worked all the way long so far.
I cleaned the tips of the optical level sensors, and I put the DC power to the Profilux 4 off a minute and on several times.
Also I checked Y-splitter and they are firmly connected and is in position.
The Profilux 4 firmware is up to date.
I have never touched any settings as well as the hardware connections in these days.
I take a look at the details of the level control settings, but all are normal.
I can not immagine this problem exacpt something wrong in the H/W inside the Profilux 4.
Regardless of actual water level, a check mark appeares after the Leve Sensor 1 and 2 allways on the level control ccircuit 1 on the MyGHL in my phone.
Is this normal?
Hard to attach image file.
Could you please help me how to troubleshoot this malefunction?

levelcont-2.jpg