Symptoms

When the user clicks on a date field button to pop up the calendar, the user sees the calendar in the top left corner of the form:

Release

Confirmed in Madrid, but can also happen in Kingston and London

Cause

In the console will find the following error:

incident.do:2644 RangeError: Invalid language tag: en.us
    at Date.toLocaleDateString (<anonymous>)
    at e._showMonth (GwtDateTimePicker.js:288)
    at e._createControls (GwtDateTimePicker.js:93)
    at e.initialize (GwtDateTimePicker.js:37)
    at new e (js_includes_doctype.jsx:3)
    at Array.<anonymous> (incident.do:2642)
    at x (js_includes_ui16_form.jsx:11103)
    at wait (js_includes_ui16_form.jsx:11103)
    at Object.runQueue (js_includes_ui16_form.jsx:11103)
    at Object.getScripts (js_includes_doctype.jsx:243)

The code is expecting "en" instead of "en.us"

Resolution

In the filter navigator go to sys_properties.list.  Search for glide.sys.language.  Check the value that is set.  If the value is "en.US", change it back to "en" which should resolve the issue.