Collaboration between customer and development team reduces in a fixed price adopting agile. Agile in fixed price project always brings a mindset in delivering the end product. So there is a thereat to a transparent communication between all stakeholders.
Quality is compromised.
Focus also in organizational profit out of the project delivery. Unlike reimbursed project where each feature development is reimbursed, a fixed price project always reimburse a fixed amount for a fixed scope. From a supplier point of view the delivery takes priority to maximize the profit over the project. This is one of the biggest challenge for agile in fixed price project.
Quality for a fixed price project always takes a back seat as the delivery team always focuses on delivering the milestone as planned to do project goal to meet both project budget and schedule. While, team plans for delivering business requirements as per acceptance criteria, at the same time the more focus on workable product and not a better quality.