Milestone development/ active sprint. Backlog is where issues begin. Todo are ready to be worked on and selected for the current sprint. Active issues are in progress. Done is ready for review. When the issue is closed it should be removed from the project.
New bugs need to be triaged. Triage includes making sure they have complete enough information to be worked on, and to decide their priority. In progress bugs are either high or low priority. When a bug or support issue is completed, and and any associated pull requests attached (bugs), it can be moved to review. Once any associated pr's are reviewed, they can be merged. If the issue is deemed complete, it will be closed and moved of the support project, or it will be moved back to high/low priority for further work. If a closed bug needs to be re-opened or re-done, it might appear in the development project and be sprinted with a milestone instead.