Deploy fails - seemingly arbitrarily

[Moggach]

The Netlify deploy fails with what seems like arbitrary errors.

The error message is

error Failed to process image /opt/build/repo/assets/jrf-prototypes-fidelity.png Input file contains unsupported

However, changing file extensions doesn't seem to make a difference - it also fails with .jpeg

Things I've tried:

• Making trivial changes to force a redeploy (I don't want to mess up the commit history by trying this too much)

• Changing image file extensions

• Looked online for similar issues - it seems as though this person had the same problem and clearing the Netlify cache seemed to fix it but I can't see that in our account UI?
  Netlify Deploy arbitrarily fails gatsbyjs/gatsby#6348
  According to this it should be possible
  https://docs.netlify.com/configure-builds/troubleshooting-tips/#build-cache

• Creating branch rolled back to last successful commit
  Branch Deploy: test-previous-build@f126dd0 - still fails

Any feedback welcome as I'm blocked on this other than continuing to force deploys until it randomly works