Garbled text with one particular feed on Android

For this feed: <![CDATA[Deník referendum]]> when viewed on Android, the article text is garbled:

It is garbled only when I open the article (in the view feed view, the initial text of all articles is clear). It is not for all articles and it seems to be consistent which are garbled and which not. For example, these ones are clear:

most others are garbled:

I assume it is something not proper that feed is doing, but still the website displays it correctly, so maybe the Android app could as well?