Context: This paper studies agile release planning in a software development organization with 13 development teams. It is important for software development organizations to be able to plan work in an efficient way that supports development work. Objective: The research aims to understand issues within agile release planning in the studied organization, and to make some improvement to the agile release planning practices there. Method: The study followed canonical action research methodology completing one cycle of diagnosis, action planning, intervention, evaluation, and learning. Qualitative methods were used during these phases to identify preliminary issues, to support the choice of action, and the evaluation of those actions. Results: The research identified issues of strain on the role of Product Owners. Sources of strain in the organization include changing priorities, the effort required to build up domain competence for new projects, and external pressure to push out new features. Additionally, there was difficulty for people participating in agile release planning to suggest improvements to the used practices due in part to the complexity and scale of planning practices in a multi-team development organization. The actions taken as part of the research provided ways for Product Owners to share knowledge between themselves, to better affect the working practices in the organization, and promoted a sense of team spirit between the Product Owners. Conclusion: Organizations should be mindful of their Product Owners when looking at their release planning practices. Problems for Product Owners are problems in planning for the whole organization. Having an active, collective, and structured channel for continuous improvement for Product Owners can help drive improvements to agile release planning.