I just upgraded to C1V10 on WIn10...I exported ~600 raw files in a LR Catalog and imported that catalog into C1V10 and all is well. Took about 15-20 minutes I think for the export. Way less to import.
Did you have exporting previews turned off?? I did.
I didn't export a new catalog, just tried to import a working catalog. I was surprised at the slow speed of importing, not sure what's going on. I guess C1 is trying to read all the adjustments etc and including them in the import
The main problem was random folders missing. Using the synchronize folder option doesn't work because it will only handle "known" subfolders, and the folders that are missing are not "known" (actually doesn't make any sense to me). I thought the only solution would be going through every folder, find out which ones are missing, and import those. I started trying that but it would take me a few hours to do it.
So I tried just importing the master folders directly into the database, assuming C1 was smart enough to not import duplicates. Seemed to work fine. In looking through the missing folders most of them appeared to be where Lr hadn't imported raw files (because they were from an IQ3 100) or where I'd move the raw files into an archive leaving only the finished tif's in the folder. So no real Lr settings to worry about, none of them were modified inside the Lr database.
So I'll give it a try, where C1 becomes my primary library program, and using ACR to gain access to Lr/ACR's far superior automask tool for brush adjustments. I would prefer to continue using Lr to manage my files, and occasional processing, with C1 just for processing, but I've given up on Lr being able to handle my IQ3 100 files ... looking like it won't ever get done.