The Magento strongly recommend that you upgrade to 2.1.7 as soon as that release is available. Magento 2.1.7 will contain a fix for this issue as well as critically important security enhancements. They provide the hotfix described in this Technical Bulletin as a temporary fix only.
You can fix this issue with image resizing by downloading and installing the CE-MAGETWO-67805.patch
hotfix, and then immediately upgrading to Magento 2.1.7, as soon as it is available.
To download this patch,
1) On Magento Tech Resources, choose Downloads > Magento Community Edition Patches > 2.x.
2) Select the CE-MAGETWO-67805.patch
hotfix.
For further discussion of this issue, see GITHUB-9385 and GITHUB-9395
Reference on DevDocs.