I found a workaround that user harriet123 posted on the Windows Central forums:
I figured out a workaround for this bug. Tap the 'listen button', it will listen without returning a result. Then lock the screen (using the hardware button). Then unlock the screen - Shazam should still be open. Try again - it should work now.
I tried this and much to my surprise, it worked on my Lumia 950. Obviously not an ideal solution since you have to do this once every time the app fully shuts down, but it's been a couple of months and with no word from the developer or Microsoft (who should
follow up on this matter IMO - it doesn't help when a major app has a problem like this on Microsoft hardware), this could be our only solution for a while.
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