If in the Blynk app the button shows as solid orange when you click it and does not turn back to hollow, then it has to do with the Blynk button setting. This may have been due to a Blynk import bug. To fix it, stop the Blynk project first (by clicking on the square stop button on the top right). Then click on the button to see its settings. The button should be set as ‘Push’ and NOT ‘switch’. That should fix this issue.