This is so lost in Agile. Engineers should get the time to “sand” their products, but we just don’t. If QA doesn’t make a ticket for the space between, it’ll never get fixed. The customer probably notices this kind of a thing but it’s a miracle if the customer bothers to report it, and another miracle if it eventually turns into a ticket, and another miracle if someone prioritises it enough to spend time fixing it. […
What does agile have to do with anything? You think waterfall explicitly provided time to test out the UI and "sand" it? This is a process that generally requires a product manager to choose to prioritize, together with a capable UX engineer and/or designer. That prioritization can be inserted into any development methodology if you want it. Agile is irrelevant here.
Sure, it is not to be blamed as per Agile manifesto but how many companies are adhering to the manifesto? It is how it is used, not what it was used for.