After Madrid upgrade, quantity selection dropdown on catalog item always shows up in the service portal, irrespective of No quantity checkbox. Even if "No Quantity" checkbox is checked the quantity selection dropdown still gets displayed on the item form on portal.
This is because "No Quantity" checkbox works only on platform and not on service portal. On service portal, in portal settings "Hide Quantity" handles the displaying/hiding of the quantity selection dropdown on catalog item on the portal.
To resolve the issue follow the steps below:
1. Navigate to maintain item > Open a catalog item (eg: Samsung Galaxy S7 Edge)
2. Click on the "Portal Settings" tab
3. Check the "Hide Quantity" checkbox
4. Navigate to the same item (eg: Samsung Galaxy S7 Edge) on service portal
Observe that the selection dropdown box is hidden on the portal.
Refer to screenshot below: