All contributions on this webform are created as recurring
You need to set a conditional to ensure instalments = 1 for the one time scenario. Instalments = 0 is open ended recurring and any other number is recurring with that number of instalments.

There was a change/PR to the repo that enabled open ended recurring contributions: https://github.com/colemanw/webform_civicrm/pull/141
so now it's even more important than before to ensure civicrm_1_contribution_1_contribution_installments is a number and set properly. It's a Number --> No is not a valid value. 

Best to keep the Widget: Number -> this is how the component config looks when it's first enabled:



If you want to hide the Element -> change the widget to Hidden and use conditionals to set its value to either 0 or 1 (based on another field).