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Error: "Fatal error: Maximum execution time of 10 secondsexceeded in /home/www/... on line ..."
If you get an error message like "Fatal error: Maximum execution time of 30 seconds exceeded in /home/www/99c0ba3d9029a7373673387482ac8c44/web/wp-includes/media.php on line 123" for example, then it's almost certainly that the page you are trying to display is trying to run a script (first displaying of a photo gallery script containing several hundreds of pictures, with creation of thumbnails and photo resizing...) that requires a calculation longer than the one authorised for each hosting.
Unblocking the memory limit (see https://faq.infomaniak.com/2121) should enable the script to do all it needs to do (refresh in the following hour the page that had a problem once the unblocking is completed), and when you go back to your page outside the period of time during which the memory limit was unblocked, the display will be possible as all calculations will have been made during the memory unblocking.