Get Simultaneously three target image with vuforia

Hello everyone,

Since 2 days, I try desperately to display 3 different objects simultaneously with vuforia. So I have 3 target image in a scene and I try to display them simultaneously on the screen of my Android mobile. However, only two of the three target images appear simultaneously on the screen. The third image is not displayed. However, I set Maximum Simultaneous Target Targets to 3 and Maximum Concurrent Objects to 3 as well.

Why can not I display the object of the third target image when I changed these values? Can you help me please ?

I have Unity 2018.2.3f1 (64 bit) and Vuforia 7.2.24

I took a screen of my scene below:

thank you in advance.