403 forbidden error Magento 2.1.2 in Developer mode only
Only in Developer mode, I am experience "403 Forbidden" errors on part of some screens:
- Products Catalog and Categories
- Customer All Customers and Now Onine
- Marketing Search Synonyms
- Content Pages, Blocks and Configuration
Everything else seems fine, only the above screens show the big 403 Forbidden message in the middle of their panels. And only in Developer mode, when I switch to Production mode, there are no problems.
I've checked all file permissions as per the docs, and I'm doing the switching between modes exactly as per the docs.
This is Magento CE 2.1.2 (recently upgraded from a previous 2.1 version).
I do not see anything obvious in any error logs under the magento directory. I have ssh access, but no sudo privs.