A site needs to be varying on cookie “user_allowed_save_cookie”. When user click “Allow” cookie, it will insert “user_allowed_save_cookie=%7B%221%22%3A1%7D;” to browser. So, it requires adding a rewrite rule to make the cache varying on that cookie. The cache needs to store two copies: one showing the yellow bar at the bottom while the other one without it.

Add the following rewrite rules to .htaccess

RewriteRule .* - [E=cache-vary:user_allowed_save_cookie]

Alternatively, most people use javascript based plugin and there is no need to set cache vary as above. The better option is to use a different cookie law plugin, then javascript will do the display based on cookie set.