I never had this before. Version 4.5.38. Default renderer, only 1400px wide, detail 0.5, AA6, 8gig used from 16 present. Took about an hour to get to this point, but then stopped. No activity anymore. Pressing stop render didn't work, didn't do anything, I could press and release it over and over. So, it didn't look like TG froze or crashed. Shutting down TG had to be forced though. Render wasn't saved in output folder either.
Low RAM available? Though unlikely - I'm sure you have at least 16.
Does the same happen when you crop-render these areas?
No, it used only 8 out of 16. I still have to try a crop, had intended to do that.
I know what went wrong. I had a GI cache file made without clouds, but then rendered a version with clouds, reading that old cache. I guess that's it. It even crashed on it just now, when stopping the render proces.
Pink color usually means an asset was not found (like a shader), so maybe that's somehow connected to the GI cache. Good you worked that out! I would file a bug report - there should be a mechanism that checks the cache against current scene state.