loadLegacyFabricCss and ms-SPLegacyFabricBlock

Hello!

I wonder if somebody knows or could help me in some way with my question related to loadLegacyFabricCss. Me and my team, we are experiencing problems with a dependency loadLegacyFabricCss. We have created some CSS classes in our solution but they get overridden by Legacy Fabric Css. Particularly a class connected to this dependency .ms-SPLegacyFabricBlock is showing in our production environment and we do not want that as it is not showing in the test environment where we create the code and test to imitate the live environment/production that our customers see. This is causing unalignment between the test environment and the production environment. Is it possible in some way to disable the legacy fabric css? We saw that adding "loadLegacyFabricCss": true, in our manifest.json meaning forcing in the legacy css imitates the production at the moment, nevertheless the other way around "loadLegacyFabricCss": false does not work. Do you know how we could disable it?

We see also that the test environment is currently on version 2311 whereas the production environment is one version behind, respectively on version 2310. May be somebody has experience with this? We wonder if this class connected to the legacy css that is causing us troubles ms-SPLegacyFabricBlock will dissapear once the version 2311 comes to the production environment. 

Thank you for any help!