As an adept and accomplished senior developer, I bring years of experience to the table. My expertise augments the gamut of your key requirements, from iOS/Android app development, and solid experience in chat server troubleshooting, to bug fixing and notification systems across both platforms.
In the past, I have meticulously resolved complex challenges just like the ones your chat server is facing: notifications not being delivered on time. I understand its critical urgency for you and want to assure you that this needs swift and precise expertise that I possess - from improving stability to addressing known bugs.
Furthermore, beyond resolving the primary issues, I'm also committed to enhancing user experience. My proficiency extends to proposing innovative solutions which can further improve functionality and streamline the user experience. Overall, my valuable skillset combined with my dedication to perfection makes me a prime fit for this project as you look forward to revitalizing your chat server.