Media browser is great for importing the clips initially. But moving between systems, the files may reside on a drive that shows with a different name in the system. On MAC, you are always shown your default folder first (not the folder where the files are, a default folder in your system somewhere, perhaps the most accessed folder or the most recent accessed one). I believe Windows starts with documents or the default as well. When you relink, the project doesn’t assume they are in the same exact pathway in the system. It allows you to specify the pathway. When you used media browser before, you probably replaced the other files with a new linked set (they are seen as separate files, not the original ones you used), and now the sequence is looking for the original linked set from your project panel. In short, you broke your sequence. You can relink the media using relink on each clip and then pointing to that clip in the file system (you have to find them). Do not use media browser when moving between systems. Use relink media. Media browser will find NEW files for import into your project. Relink will use your system file manager to allow you to search for and find the files to relink to the entry in your project panel. When you used media browser before, you simply imported new entries, or you had it “replace Footage” or something like that. It’s great for bringing in new files, not for re-attaching the pathways. I can’t say it enough. The behavior is perfectly normal.
Remember:
Windows sees drives by a letter and then a pathway.
Mac sees by /Volumes/drivename/Pathway or by a unix style /dev/mnt/sda/d0s1/pathway styled path.
Moving between them requires relinking media, and after effects comps etc. It in no way involves the media browser…