Background: By creating ecosystems around platforms of Open Source Software (OSS) and Open Data (OD), and adopting open collaborative development practices, platform providers may exploit open innovation benefits. However, adopting such practices in a traditionally closed organization is a maturity process that we hypothesize cannot be undergone without friction. Objective: This study aims to investigate what challenges may occur for a newly-turned platform provider in the public sector, aiming to adopt open collaborative practices to create an ecosystem around the development of the underpinning platform. Method: An exploratory case-study is conducted at a Swedish public sector platform provider, which is creating an ecosystem around OSS and OD, related to the labor market. Data is collected through interviews, document studies, and prolonged engagement. Results: Findings highlight a fear among developers of being publicly questioned for their work, as they represent a government agency undergoing constant scrutiny. Issue trackers, roadmaps, and development processes are generally closed, while multiple channels are used for communication, causing internal and external confusion. Some developers are reluctant to communicate externally as they believe it interferes with their work. Lack of health metrics limits possibilities to follow ecosystem growth and for actors to make investment decisions. Further, an autonomous team structure is reported to complicate internal communication and enforcement of the common vision, as well as collaboration. A set of interventions for addressing the challenges are proposed, based on related work. Conclusions: We conclude that several cultural, organizational, and process-related challenges may reside, and by understanding these early on, platform providers can be preemptive in their work of building healthy ecosystems.