PSB files corrupted by changing metadata

Since using Lightroom classic on a mac I have had problems with large photoshop (3gb plus) files corrupting when I add final metadata in lightroom. What may be happening is that because the files are big it takes time for the metadata to be save and if I change the filename the file becomes corrupted. Or it may be that I am opening the files for final checks in photoshop before the metadata is properly saved to the files. As lightroom seems to chang the metadata in the background I have no idea when the metadata has been saved. Either way I am getting far too many corrupted files after a final metadata change before despatching the files. When trying to open the corrupted files the error says that one or more layers are corrupted and photoshops asks if I want to flatten the image after which it says the file is an unrecognised format. These are .psb files. Any ideas or is this a bug that needs looking at as I am loosing too many hours re-doing difficult images? Thanks Paul Williams