Mod Version: yawp-1.19.2-0.0.2.9-beta3-forge
Forge Version: 43.3.13

Created a large region with flags "break-blocks", "access-containers", and "place-blocks". Created child region. Removed "access-containers" flag from parent. Players still unable to access containers in children. Admins seem to receive correct flags, and are able to access chests, but not break blocks.

My mistake, I had a section of world spawn clipping into the region, causing some confusion. Moved worldspawn and flags worked as intended.