IOS adding a new Adjustment Brush not working like Radial Filter or Graduated Filter

I am using LR Mobile 5.3.1.53 B120.  I have an iPad Air with 128GB with around 50G free.  Around 3 weeks ago I  changed from the Creative Cloud Photography 20GB plan to the Creative Cloud Photography 1TB plan.

In the last 48 hours I noticed that creating a new Adjustment Brush has stopped working - it is as if it brings about almost no change.  I have carried out the following tests on both RAW and JPG images

1. On a photo taken at night
   1. I can add a graduated filter, see a very bright pink/red area showing me the area that will change and I can then turn the black sky into white by increasing exposure etc
   2. I can add a radial filter, see a very bright pink/red  circular area showing me the area that will change and I can then create a white circle in the night skyby increasing exposure etc
   3. I can add an Adjustment Brush, and all I ever see is a blue diamond.  No bright pink/red area is painted under my moving finger, I think there is a very vague hint of pink, the dark sky does seem to lighten ever so slightly, but it is about 1% of what it used to do 
2. On an overexposed photo
   1. I can add a graduated filter, see a very bright pink area showing me the area that will change and I can then turn the white sky into black/very dark grey by decreasing exposure etc
   2. I can add a radial filter, see a very bright pink circular area showing me the area that will change and I can then create a very dark circle in the overexposed sky by decreasing exposure etc
   3. I can add an Adjustment Brush, and all I ever see is a blue diamond.  No bright pink area is painted under my moving finger, I think there may be very vague hint of pink, the white sky does darken ever so slightly but nothing like it used to

2 days ago I edited a photo with multiple Adjustment Brushes - the photo was taken on a very sunny day with deep shade under trees.  These brushes worked exactly as I have always known them to work.  That is if I am careful I can change the light in different areas and produce a nice balanced photo.  And of course if I  drag any of the light controls to their extremes I'll get a white-out or a black-out.  

As a final test I went back to this photo imported and edited 72 hours ago on the same iPad

1. I can select each of the adjustment brushes I added 72 hours ago, I will see no pink to show the area that the brush will work on (yes the option to the highlight is turned on) and 
2. I can adjust the lightness/darkness/colour etc as I was always able to
3. If I add a new Adjustment brush, then nothing happens - no pink area, no appreciable lightening/darkening no matter how large the adjustments I make

I have closed the app and restarted it, I powered down my iPad and restarted it.  It makes no difference to the above behaviours.

Does anyone from Adobe who monitors these posts have any ideas what is going on?