I just streamed from an Android phone with the Blue TV app 5.3.4 to a Chromecast and couldn’t understand the problem. Even the blockbuster Men in Black, which was shown on RTL2 last night, worked without any problems.
Maybe it’s a temporary problem that has now been fixed?
If not:
Which blueTV app version are you using?
What connection between tablet and screen?
[Addendum] A series from 2015 via blue play (i.e. paid content) also works. [/Addendum]
[Addendum2]
@Tux0ne According to your nickname, you also have Linux. Does it work there with DRM turned off?
Chromecast supports DRM, so you should be able to see something there even with vision protection activated.
[/Addendum2]