built a simple web site with logo and 6 pictures across horizontally below logo.
attempted to slide to breakpoint at phone size and pictures did not stack as I hoped 2 per row horizontally.
Manually did it and saved project.

Went back to large display and it completely changed and screwed it up........Have I missed something. ???

We won't know if you missed something until we can see your project file. Please zip up your .rsd file and post it here.