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I installed the backup local, uninstalled the template and made a fresh installation. After that everything worked fine. I installed my custom.less and custom.css and after that I rebuilt the template in the template designer.
After finishing my work I tried to save my custom style and the template crashed again 🙁
Now I have two ideas :
1. Could it be possible that the saving process of the template executes the error? Could this be part of the problem with the old php Version?
2. Or could it be the problem, that I put most of the grids all in one container? I stored them all (20 grid positions) in the main container. The site is build as a onepage website but with lots of content so that the onepage theme is not sufficient. Perhaps the saving process is to great and the error occurs? In this area I have not much knowledge but perhaps it is a hint for you...
My next step is to install a backup local with the new php version and start the process again - fresh template, make my changes, save my style and see what I get.
Please give me a note if you have an idea to my suggestions.
Thanks, Orti