A really long post name for a simple problem. Another bug caught my attention today and I was so amazed by it I thought it deserved a post.
If your ‘+’ button on the Opportunity Product subgrid on the Opportunity product doesn’t work anymore, change the name of the grid back to opportunityproductsgrid.
That’s it. Another weird bug solved.
Solution was found here on the Dynamics Community forum: https://community.dynamics.com/crm/f/117/t/176528?pi51685