I have overridden standard 'Add Products' button of OpportunityLineItem object with a VF page. It was working fine in classic and Lightning both before Spring'18 release. But after Spring'18 release it is working only on classic. In lightning it is redirecting to the standard detail page of opportunity. Is this any issue with Spring'18 release or am I missing some settings for button override.
Best Answer
As, I have observed that on Opportunity product object under Button and Links there exists two buttons for Add Product as per below screenshot
1st button with Name AddProduct is configured on Salesforce classic. and the other button with Name MultiAdd is configured on Lightning experience.
So as per my understanding, you need to override the VF page on second button as well. Please verify and let me know if that works for you.