Clicking any option in the texture editor causes the engine to freeze on mac os 10.12.4 and 10.12.5. Tried this on both 4.16p2 and p3, on two different macs.
Also the material editor takes a lot longer to load than it used to.
UP
Same issue here, with the public 4.16 version on Mac OS 10.12.5
Yeah, turns out this is about mipmaps.
Render targets work fine - I can change the resolution and various settings, and static textures created from render targets work fine until I set their mipmap settings to anything other than “no mipmaps” - initially they have none.
With some imported textures, I can set the mipmap setting to no mipmaps, and after that they work fine.
But I can’t do anything with the textures that have mipmaps. Whatever setting I touch causes a freeze. (Not a crash)
Then I just have to force quit. I searched for the logs, but couldn’t find anything relevant in there.
I probably never said “mipmaps” so many times before 
exactly the same
This seems to be fixed with the 4.16.1 hotfix. Texture editor still feels a bit slower than it used to, ie. takes a second or two to do the calculations, which was instantaneous, but it doesn’t freeze now.