I'm also noting a generic pattern of intermittent response times in pretty much anything serverless.
When you take a traditional tech stack, say LAMP on a dedicated server, performance is very constant overall. You even develop a type of muscle memory for it and adapt a click pace/flow when you use an application like that intensely.
No so much with cloud-native serverless. A page may respond fast and then 10 times slower the next time. There's just so many moving parts (virtualization, edge, cache, cold/warm compute, out of network dependencies, etc) that it feels random to a user.