We just upgraded to Moodle 3.4.1+ and installed the Essential Theme, but sometimes we got an blank error message when accessing the page:
It appears on random pages while loading/refresh them (Course detail/dashboard/Student list. etc.)
The same is happening on different browsers. Sometimes there are more windows like that opened and you have to click on "X" to close them to access the page, but then it works normally.
Any idea how to fix that?