Describe the bug
It is not a plugin issue. The QgsMapLayerComboBox doesn't show layers on QGIS 3.14. It works on the previous versions of QGIS.
How to Reproduce
QgsMapLayerComboBox will not display any layer as reported here with screenshots:
https://github.com/romariocarvalhoneto/Weighted-Multi-Criteria-Analysis---WMCA/issues/5#issue-647074618
QGIS and OS versions
Works on the previous versions o QGIS. Don't work specifically on version 3.14.
Additional context
Confirm.
Can you share sample code which demonstrates this issue? This widget is used everywhere in qgis, and there's many unit tests covering it.
This is a downstream plugin issue - see comment on referenced bug report