Google sheets: =SUM shows incorrect fraction

When doing a simple sum of cells in google sheets, the result is being reported as a fraction somehow? And the values make no sense? Does anyone know why this is happening?

In the pic below, you can see the values of the cells, the formula entered, and the preview of the result to the top left of the formula:

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Here's another one where summing 1,2 and 3 is reported as 1/5:

pic