In short: A slew of users on reddit are experiencing slow reaction times from Google Assistant when using its wake up commands, "Ok Google" or "Hey Google". Others are also experiencing slow reaction times when giving Google Assistant commands. This could be an issue on Google's servers and should be resolved shortly. Many are stating that this started on Monday, and has continued.
Background: With the Google Assistant, you can say "Ok Google" or "Hey Google" to wake up the Assistant and then give it a command. Typically it is pretty instant at waking up, either with a tone, or by showing the four lights on a Google Assistant-powered speaker. Then you can give it a command like "How's the weather" or playing a certain playlist on a specified music service. Though, Google Assistant taking its time to respond to the user can usually vary based on the local network, if you're on a slower network or the speaker is further away from the router, it could take longer due to the speed that it has - this is because Google Assistant does need to ping the cloud to do many things. But if the network hasn't changed at all, then it obviously isn't the network here. Not only is Google Assistant responding a bit slower, but it is also failing to do certain commands that it has done before.
The impact: This is going to frustrate users, as they will have to wait longer to give Google Assistant commands, but it shouldn't affect the experience too much. Though with some commands not working at all on Google Assistant, that would definitely affect the experience. Hopefully this is something that Google is able to fix in the next few days or sooner. It shouldn't be a big issue for Google to fix, and likely won't even need to push out an update to Google Assistant devices.