In Industry 4.0 and 5.0, humans and robots share physical and social spaces, making sustainable workplaces essential. While mobile, flexible, and collaborative robots offer new possibilities, challenges remain. Effective human-robot interaction relies on mutual recognition of actions and intentions for efficiency, safety, and smooth collaboration. Awareness of user experience (UX) is growing, as it influences work satisfaction, engagement, and well-being. This paper identifies UX issues when mobile robots are introduced on the shop floor alongside operators and truck drivers. The study, conducted at a large manufacturing plant, examined mobile robots delivering heavy parts to the assembly line and navigating a busy warehouse corridor and production area. Two months after field testing, a post-evaluation took place, with data collected from eight participants, four operators and four truck drivers, who had frequently interacted with the robots. Participants completed a questionnaire and an interview. Key findings show: a) differences between operators and truck drivers, b) higher UX assessments for operators, c) more and greater challenges for truck drivers, and d) neither group seeing major personal benefits but recognizing advantages for the company. Both physical and cognitive work environment problems were identified.