Android 7 and problem with Hey Google in Google assistant

Hello.
Today I've encountered strange problem with My Google Assistant. Some days a go It worked also with Hey Google, but It stopped to work.
I've tried to fix this issue with similar things, like It is described on internet from Google assistant settings, also I've switched My mobile from Slovak to English, but It didn't help.
What should I do? I think to finally buy mobile with some new Android OS and It is an other reason, not just Podcast addict, but also this. Or, have You encountered It too?
I know, that I can activate It by holding touch screen button, but I love to activate It by very known voice command 'hey google'.
Marco