@Ashley, as the problem is intermittent at best it will be hard to do this I think, but if I can reliably reproduce the problem I will email you a shared link where you can download the project which is just my file working through the Building a platform game - a beginner's guide
By the way, in the interim is there a log file that Construct 2 logs errors to which might give you an error signature to help with your analysis.
On a completely different error, but for the same .capx file I just received this error when I tried to run the game which I cannot fix by saving to another filename etc as I did before:
'HTML5 exporter - Error during export: Cannot open file 'C:\Users\John\AppData\Local\Temp\c2-2BD38M\html5\data.js'
So then I saved this .capx and tried to open it and and I got another error:
'Failed to load texture - Error loading texture 'C:\Users\John\AppData\Local\Temp\cap2MF79F\Animations\Flooring\Default\000.png': Failed to read image file data. This may indicate a corrupt PNG file in the project directory. The image will not be able to be displayed in the editor.'
To this end, I am emailing you a shared link where you can download the .capx file so you can see where I am at now.