Brandywine flower drop

[Inamon]

So all of our tomatoes are growing very nicely including the brandywines, with the exception that the brandywines are dropping their flowers before the onset of fruit.
By this I mean that the whole flower head is dropping off at the elbow. To me it looks like the flower stalks would be too small and weak to hold the fruit if they did set, looking more like cherry tomato stalks rather than the robust stalk of a beefsteak/big boy.
Is this a common problem and what can be done to resolve the issue.