SPPB Feature block addon causes sections to overlap when displayed on mobile

I had a home page sppb 5.3.4 beginning with a section made of one row with 4 feature block add on. A second section made of one row with one image add on and one feature block addon.
Display on laptop was ok, display on mobile not: the second section overlaps the first one.
I made some changes and replaced the first section with 4 feature block add on by the same section with 4 image add on. The display is ok now on mobile. The question is: why it doesn' work with feature block add on? and it is ok (in term of display) with image add on.
In my case, i did not use interaction from the concerned feature block add, so i made a copy of the display of each feature block addon as image, and put this image in image add on. But it is some tinkering.....
Regards
jluc