Hi @ysipahi,

This is a CSS conflict with the theme or other plugins. One of those adds {display:none} CSS rule for all buttons, so the post comment button is invisible too. 

Please watch this video to better understand what I mean:

https://www.screencast.com/t/AvLlImgn

This CSS code should help you to solve the issue: 

#wpdcom .wc-field-submit input[type="submit"]{
     display:block !important;
}

Put the code in the Top Admin Bar > Customize > Additional CSS > "Additional CSS" textarea, save it, delete all caches and check again.

thanks, I see but where is this top admin bar?

Thanks, I did just the same but + cleared the cache but still the same..

Many thanks now it is solved..