Most often, delays are caused by network issues, between your controller and router, or the router and the speakers. I’d certainly check the wifi interference FAQ, as well as performing a Sonos network refresh, by unplugging your Sonos devices from power (or powering them off, if battery connected), and rebooting your router. Once the router has recovered, power back on your Sonos devices. This will give them both a fresh IP address, as well as a refresh of the Sonos OS. Finally, check your system for updates, in case there are any that need to be applied. 

If the above doesn’t work out, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. But don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Unfortunately,  this did not work. Now, I found that my connect amp has a red light blinking. I've restarted it several times without positive result. 

The mentioned delays disappeared when removing power from the Connect Amp.

It may be that there is an issue with the CONNECT:AMP, I would call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.