Hi
The support from weeblr provided a fix for this problem
Here is a step by step list to fix it
1. get the latest version of sh404sef (you can get a dev Version/soon they will bring an official new version but this dev version from the link fixes the problem
Dev Download sh404sef and install it
2. make sure in settings> sh404sef> components> sppagebuilder is set to use sh404sef router (above i have added a screenshot so you can see this setting. Its very important to set it this way as mentioned by the developer of sh404sef!
3. then delete all sppagebuilder pages that are collected in the sh404sef> SEF Urls (no worry they come back later)
4. turn off sh404sef & save and turn on again (i did this it was not adviced by the developer)
4. Clear cache
5. visit the pages so they appear again in sh404sef> SEF Urls
6. try the Preview and Front end Buttons
7. Now everything should be fixed
It did work for me at two pages on different servers
Please give Feedback if it also did work for you
Thanks