Hi
When we upload floor image to visualRF, it will divided in to more than 2000 grid cell in backend and all cell have same (x,y) measurment value.
VisualRF colors number of grid cell based on transmit power value and singal strenght, if grid cell size is large and -55dbm singal strengh does not reach the corners of the single grid it wont show any color. I checked the heatmap screen shots which you have shared, it looks first floor map grid size is large because of that you are not seeing proper heatmaps.
Note: Make sure while uploading image try provided accurate height/wedith mesausrment values.If image is already uploaded you can set measurments value using resize option.