Good question. In the case of delayed replies, it's really getting worse. We often think she didn't hear and start asking again - she heard and she's just thinking about it. Home internet and wifi are fast in general.
They've also been reducing the level of acknowledgement intentionally over time - sometimes I will hey siri on my airpods and think it didn't hear me, only to be hit with a "yes?" a few seconds later.
That's weird I have not experienced that issue. Alexa is pretty responsive for all my queries. I use it every day but mostly just for setting kitchen timers.