First, I would recommend that you follow our Update Guide at https://theme.co/apex/forum/t/setup-updating-your-themes-and-plugins/62. The most important point in there is you the setting up of a staging server to test the updates.
If this happened to your live site, you will need to decide whether to update or not. If your site's working perfectly fine with the old version, I'd recommend that you delete the new version (2.3.6). But, test Pro 2.3.6 in the staging copy of your site so you can uncover issues and report it to us. This would be the safest way.
Regarding the child theme, it will use the new version so if there's no issue in your site right now, you can delete the old version.