I think I know what is causing the lack of basemap that you saw in the screenshot - the basemap isn't loaded when hardware acceleration is OFF, at least when I tested and troubleshooted in Chrome. When you turn on "Use hardware acceleration when available", it loads the basemap just fine. For anyone who wants to fix it in Chrome, it's in Settings > Advanced.
I do have (and have always have had) hardware acceleration enabled in Chrome, so I don't think that is the problem.
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The sequence of events surrounding this issue goes something like this:
When dashboard page reloads, the overall canvas initally fills only 2/3 width of my screen, and the content of containers is in imperial measurements - the map container at this stage is empty (grey background)
Then the canvas refreshes with metric values - the map container is still empty.
Then the map container starts building the map background - sized to fill the map container (while the canvas is still 2/3 width of screen)
As the map is still building, the canvas expands to full width of screen, the map container expands both vertically and laterally, but the map background only expands laterally (ie it stays the same height) - map background at this point is centred vertically in the map container.
Lastly, the map background (in its original height) is moved upwards to align with the top border of the map container - leaving the display looking like that posted by WSWeather.
Hope that all makes sense.