Which system version is running on your Mac?
Have you tried to find out more about the items, that are causing the freezing? What is the format of the items that you cannot open? Videos? Jpegs, or another image format? Can you export the items with "File > Export > Export unmodified original" or is this resulting in an error message? If yes, what is the error?
If you have "My Photo Stream" enabled, the "All Photos" view is all containing the My Photo Stream photos. Try to find the photos you want to open in the Days, to be sure, they have been downloaded from iCloud.
How much free storage is on your Mac? And where is your photos Library stored?