Help! cache_render grows extremely big in Drupal 8

Good morning

I am having a big problem with a newly created Drupal 8 site for a theater.

After going live we discovered that the cache_render table grews extremely big extremely fast. After one weekend, it was already over 30 GB (!) which makes a backup of the database impossible.

After some analysis and google search I have stumbled upon this stackexchange post http://drupal.stackexchange.com/questions/201663/cache-render-database-t...
They say it is wise to use a caching service such as Memcache but honestly, that does not really solve the problem at all.

I have set the Cache maximum age to 1 hour and the cache_render page STILL sets the expiration date to infinity! Why?

What causes Drupal to fill up the database this much?
Why is this happening?

Please help.

System information:

Drupal version: 8.1.0

Modules in use:
- color_field 8.x-2.0-rc1
- contact_block 8.x-1.1
- contact_storage 8.x-1.0-beta4
- ds 8.x-2.3
- embed 8.x-1.0-rc2
- entity_embed 8.x-1.0-alpha1
- entity_reference_revisions 8.x-1.0-rc6
- field_group 8.x-1.0-rc4
- file_entity 8.x-2.x-dev (2016-Apr-13)Aktuell Ok
- Google Analytics 8.x-2.0
- google_map_field 8.x-1.1
- imagemagick 8.x-1.0-alpha2
- layout_plugin 8.x-1.0-alpha22
- mailchimp 8.x-1.1
- menu_link_attributes 8.x-1.0-beta1+5-dev (2016-Feb-23)
- metatag 8.x-1.0-beta8
- paragraphs 8.x-1.0-rc4
- smtp 8.x-1.0-alpha0
- token 8.x-1.0-alpha2
- weight 8.x-3.0
- yoast_seo 8.x-1.0-alpha2+2-dev (2016-Mai-20)