Experienced this several times, it happens after package or Editor update (project upgrade to new Editor version), not sure exactly when. Don't know how to fix it. One time had to reinstall package, reinitialize and rebuild groups from scratch. But as project grows it is too cumbersome to do it every time it breaks :/. Built In Data group disappears also. It is still there, in AssetGroups folder, but how to put it back?
Updated a few third party packages today and all my addressables catalogs disappeared. The AssetGroups still appear in the project hierarchy, but addressables window is empty. A warning appears: "Schema asset already exists at path Assets\AddressableAssetsData/AssetGroups/Schemas/0bb04a299accfcb468830088e6e12838_PlayerDataGroupSchema.asset, relinking." All my asset groups seem to be missing schema links. There's a few schemas under the schema folder, way less than the count of groups I have though. Teach me not to backup before updating packages... Edit You can add your groups back in by editing AddressableAssetSettings.asset in a text editor. Add your groups under m_GroupAssets, the guid for each group is found in its meta file. Then restart editor and seems to work.
Which text editor you use to edit .asset files? However, i found that if you select AddressableAssetSettings and set Inspector mode to Debug, you can change Group Assets array. Just increase its size and link missing AssetGroup-assets.
Happens to me a few times too, already tried many things but still happens. This also results file loss, the corresponding addressable files are also removed at the same time. I have to revert file changes in git, and restart Unity.