Today while updating I received:
:: Starting full system upgrade... resolving dependencies... looking for conflicting packages... :: python2-pyqt5 and pyqt5-common are in conflict. Remove pyqt5-common? [y/N] y :: python2-pyqtwebengine and pyqtwebengine-common are in conflict. Remove pyqtwebengine-common? [y/N] y
I removed both and all seems fine. This must be related to Arch cleaning up python2.