mint 18.3xfce/win7 - sony laptop - keyboard backlight bizarre behaviour : not working on boot, working after sleep resume.

Hello, I would like to ask your help about the keyboard backlight of my sony vaio sve-1711x1e. dual boot mint 18.3 xfce/win7.

I tried to put everything in the title but here is more background story.

The keyboard backlight doesn't work on boot, but works perfectly fine when i resume from sleep.

Expected/normal behaviour : Like on seven : press any key and it lights on for a few seconds before fading out. There is no hardware key or switch to turn it on or off or change the keyboard backlight brightness btw.

It was working fine on ubuntu-studio 14.04, then started to have this bizarre behaviour on ubuntu-studio 16.04 and never stopped (tried it on ubuntu 17.04 as well).

Now on linux mint 18.3 it still has the same behaviour : the keyboard is lit on boot until the mint logo disapears, then it fades out and never turns on again.
If i enter sleep mode, and resume, then it will always work perfectly fine.

What I tried :

change /sys/module/sony_laptop/parameters from -1 to 1 as seen on another forum

create sony-laptop.conf with "options sony-laptop kbd_backlight=1" in modprobe.d as seen somewhere else

played with xset led commands as well.

no result...

the keyboard backlight seems to cause many issues on laptops with linux...
i would love to dig this out and find out especially why in my case is it fine after a suspend and not on boot, but i'm such a noob i can't really understand what to do...

nobody never heard of such a behaviour for devices working only after a suspend ? this might help.

I already asked this on a french mint forum as well as the global mint forums, they didn't have a clue so one more step further !

One last word : I am very new here, but I am not a kid, I have 5+ years of ubuntu behind me but I never had to ask anything on a linux forum, I'm not sure what to add here but please be kind to ask me any more info you'd need with the minimum direction on how to obtain them.
Please consider me a noob but I really want to learn, and I really want to fix this, even if I have to dig deep, I love this laptop.

Thank you very much for your reading and depending on the time zone, have a sweet night or a very good day.