Functional bugs are related to a functionality. If a button doesn’t work, the search doesn’t react to the user input, if an app crashes or a product detail page isn’t or not properly displayed – it’s a functional issue. Every time you click and the website/app doesn’t respond as it should, it’s probably a functional issue.
If there are elements out of place or pictures with bad quality, it is not a functional bug.
Functional bugs have three priorities:
Low: Minimal impact on user experience
High: Serious impact on user experience, but doesn’t prevent the function of the app or website.
Critical: Preventing a function of the app or website, Causes a potential loss of income for the company running the app or website. e.g. an app crash.
Critical issues like crashes etc. should contain crash logs as part of the documentation.
Edge case bugs are never critical, even not if they are crashes.
And edge case would be if: You start an app -> minimize it -> change device setting -> Open the app again. Basically, every bug that is forced is an edge case.