the histogram is not rendered in ubuntu - formerly reported in T22592 but seems to be a general problem
@kirchnth: it worked with Qt 5.8 under linux, right?
@goch: is raising the minimal version of Qt to 5.8 in MITK reasonable?
It worked with Qt 5.7 on my Ubuntu VM.
Tested it with Ubuntu and Qt 5.7 on an older master. It works.
Recently, due to T24011, Qt 5.10 is needed for successfully display the plugin (independent of the OS)