"Flickering effect" in PPAPI Adobe Flash contents - MacOS High Sierra 10.13

Hello everybody,

I have an issue with Adobe Flash Player:

I am using a software which shows Flash Player videos & animations and I have the following issue:

When I try to read a Flash content, I can hear the sound perfectly, but the screen remains blank (white). If I go fullscreen, after a few seconds images start to appear     but there is an important "Flickering/Blinking" effect. For a few miliseconds the screen will be all blank (white), then the image of the content I am watching will appear, then it will become blank again, etc... at a quite high frequency (several times a second). It is a kind of "stroboscopic effect". If I leave the full screen mode, the same issue (blinking) will continue.

I am not sure about this information but I believe the software I am using is based on the Chromium browser as I've seen a file named "Chromium Embedded Framework.framework" in its installation files.

I am requested to have the PPAPI installed to be able to use the software, so this must be a PPAPI issue.

Video of the issue:

I have the following Flash-related elements installed on my MacBook:

     27.0.0.170 :NPAPI

     27.0.0.170: PPAPI

My system:

     MacBook Air

     MacOS High Sierra 10.13

     Core i7

     8 Go DDR3

The software used to watch the flash content:

     ATP Digital (their website: bristol.gs)

I already tried to:

     - Reinstall Adobe Flash Player (version 27)

     - Install an older version of Flash Player after uninstalling the current one (version 21)

     Without any success so far.

In case this information can be helpful, I have two web browsers on my computer: Safari & Google Chrome (but I only noticed issues with ATP Digital so far).

Is this a known issue? Is this related to MacOS HighSierra? Are there any workarounds? What can I do?

Are there some tests I can do to try to identify the root cause ?

Thank you very much in advance

Greg.