In ...\Modules\AppUtil\src\mitkBaseApplication.cpp ln 531 the QStringList of pre load libraries is joined with "," to a QString.
d->m_FWProps[ctkPluginConstants::FRAMEWORK_PRELOAD_LIBRARIES] = preloadLibs.join(QString(','));
But in ctkPluginFrameWorkContext ln 119 a QStringList is expected with pre load libraries as items but a due to the join a QString is received.
This leads in the end to an error message "Pre-loading library <preloadlib1>,<preloadlib2> failed: <...> Check your library search paths.". because the previously inserted QString <preloadlib1>,<preloadlib2> ends up as one item in the QStringList.
-> So multiple libraries currently can't be loaded.
Solution is to remove the join command and to insert the QStringList in mitkBaseApplication:
d->m_FWProps[ctkPluginConstants::FRAMEWORK_PRELOAD_LIBRARIES] = preloadLibs;
This way the QStringList is inserted to the QVariant and later on also reveived withing ctkPlugionFrameworkContext.
I will create a pull request on my mitk github fork for it once I have the bug number.