I activated aggregate CSS on my local development and on a remote testing environment without any problems. Now on staging the aggregation of CSS files causes trouble: on some pages the styling looks correct but on random pages it is completely broken. The HTML sometimes shows:

<link rel="stylesheet" href="/?p0upgh" media="all" />
<link rel="stylesheet" href="/?p0upgh" media="all" />
<link rel="stylesheet" href="/?p0upgh" media="print" />

Sometimes some of the aggregated files seems not to be inserted via HTML meaning: there are no Tags or just one - some of the stylesheets are missing.

I checked folder permissions: sites/default/files and sites/default/files/css have 777 as chmod values. The owner and the group of the folders and files belong to the correct folder and CSS are aggregated in sites/default/files/css.

Does anyone has some hint for me what my cause this problem?