RW7 issues - not rendering properly

I am having real problems with RW7. With both 7.02 and 7.04. Basically its is really flaky at rendering pages for publishing. Mac is on 10.11.6.

It seems ok at first then I find I add an extra stack and it wont preview properly. I have tried using both UIKIT and Foundation (am on latest release of both) and they both have issues. I don’t know what is going on. Cant seem to understand what is going on.

I have just tried rebuilding a project that was failing in RW7 and copying the stacks over to RW6 and it now previews perfectly.

Is anyone else having such issues - any ideas.