This is an overlay problem.
You had opened an overlay and probably tabbed out and in, resulting in it being invisible. Though this is not always the exact reason why it happens, all overlays are non-compatible with Overwatch therefore any malfunction that happens with them is not on Blizzard.
Blizzard’s policiy is also that they do not refund any SR, you can read more about that here: Overwatch Technical Issues, SR Loss, and Leaver Penalties
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