Guys can we focus this thread onto this photos issue? It seems to be reproducing amongst other users. ACPI is not related.
For those testing, can you
1. make sure you backup the photo library so you don't lose all your data
2. create a new library by holding down 'option' key when opening photos. Create a new library
3. Delete your first photos library (if you're unsure its the one in photos preferences that has 'use as systems library' greyed out.
4. Open up your new secondary library and check in photos preferences that 'system library' is NOT selected/greyed out.
From my testing so far, Mac will NOT freeze if there isn't a systems library. I don't know why.
I, or someone else, can test whether importing new photos into the new library and selecting systems library also works, or not.
I am hypothesising, somewhere we have corrupt photos libraries. I personally have transferred my library over from iPhoto and there might be a bug.
I can't spend all this time testing, need other users to join in, replicate, and someone with more computer brains actually work out whats happening.