Enumerations objects are undefined in plugins with Qt 5.12.4
The issue is reproducible for me in my builds with Qt 5.12.4 but not in AppImages (that use Qt 5.9.3) so this may be related to Qt version. But this is seemingly reproducible not exactly always.
Steps to reproduce:
1) In Plugin Manager activate the "random" standard plugin.
2) (optional) restart MuseScore
3) Click Plugins→random in menu.
Result: empty score appears. Console says something like that:
unknown:unknown: QMetaProperty::read: Unable to handle unregistered datatype 'Ms::PluginAPI::Enum*' for property 'Ms::PluginAPI::PluginAPI_QML_88::Element' file:///home/piton/p/musescore/build/musescore/share/mscore-pr-3.1/plugins/random.qml:unknown: file:///home/piton/p/musescore/build/musescore/share/mscore-pr-3.1/plugins/random.qml:38: TypeError: Cannot read property 'TIMESIG' of undefined