How to replicate:
Have raws imported on iPad (stored locally, but shouldn't matter as imported on mobile)
In rating (star mode), zoom to assess sharpnesses.
At first, the picture will be rendered, but then GETS blurred or degraded
The only way to render again, is to switch to develop mode
See video attached (sorry, haven't recorded the actions but you clearly see the image getting blurred)
The two screenshots show the status in rating mode (blurred) and then corrected right after having switched to develop mode.