The default state for Comment bubbles when zoomed is to be enabled.
When blueprints are updated from previous to 4.18 they are automatically assigned as true to all comments. This means that you would need to goto every comment, albeit via the Find functionality, and set it manually to off.
In some cases this could be thousands of comments over many files.
It would make more sense to have a global setting and then have the local setting to false by default. The local setting can be used to over-ride the global setting.