"Webpage not available" for some webpages but not all

I can not access all webpages on my phone. While some are working fine, others simply show "Webpage not available".
This appears to be independent of the webbrowser. It's always the same webpages that won't work and they won't work with neither mBrowser nor Tint Browser and I have also experienced this on my mother's smartphone with the default browser.
This is not a matter of misspelling or being temporarily not available: I have been experiencing this for months now (not always - there were times when I was able to access those pages) and the webpages are reliably accessible from a computer.
This happens both when I am entering the URL manually as well as when clicking on a link from google.

Removing the battery or clearing Tint Browser's cache did not help.

some pages that are not accessible:

• https://wiki.archlinux.org


• https://github.com


• https://jisho.org

some pages that are accessible:

• google


• leo.org


• wikipedia.org

I am using Android 4.0.4 (CyanogenMod 9.1.0), mBrowser 12.0, Tint Browser 1.8 (10). My mother's phone was a Sony Experia with the preinstalled OS but I can't check the Android version because it got lost.