Cache settings in advancedsettings.xml appear not to work

RPi2, Libreelec 8.01

While watching content from the internet I get off and on the new form of buffering. A few versions of Kodi (XBMC) back it used to properly stop playing and wait till the buffer was filled up again and then continue playing. But with the more recent versions of Kodi I see often that the video playback goes into some kind of slow motion and the sound disappears.To reduce this I have tried to set a larger buffer size. I have created the file /storage/.kodi/userdata/advancedsettings.xml and put the following text in it:

<advancedsettings>
<cache>
<buffermode>0</buffermode>
<memorysize>139460608</memorysize>
<readfactor>10</readfactor>
</cache>
</advancedsettings>

However, if I check the network usage when I start playing video via internet in a add-on, then I do not see at the start increased data transfer to fill up the cache. It appears to be the same as without the settings in advancedsettings.xml. Any idea what I am missing to enable the cache settings?

Should the setting in advancedsettings.xml have effect on video playback in a add-on (Uitzendinggemist (NPO)) or will the add-on override the settings?