You should fit Phabricator a try (there is a community fork at https://we.phorge.it ). It is fast, simple, yet powerful. Basically the best ticketing system, I've worked so far.
I’ve been looking for various software for a while as a potential replacement, and after looking at a variety of open source tools for different parts of our devops process (code hosting, CI, ticketing) I’ve realised that, bigger more well known projects have the best integrations with other tools by far, and also due to their integration between features have the least friction when using day to day.
I’ve lately been looking to GitLab, which looks like it has the middle ground between simplicity of task management, and complexity with a billion features and concepts like Jira. Does anyone who has used it extensively have any experiences to share?