I have LR 5.5 installed on my MBP and Mac. My usual workflow is to export the (Smart Preview) photos for editing using the Export as Catalog option, edit them on the MBP then re-iport them into the main catalog on the Mac.
Having updated both machines yesterday, I edited 150 exported photos on the MBP then tried to re-import back into the main catalog on the Mac. I was stuck with the message "checking for duplicates" for 12 hours and eventually had to kill the process as it was taking 100% cpu.
This has not been a problem on any previous versions or updates having used this process since it was introduced.
Anyone else having the same problem, or suggest a solution?