I don’t know what to do here. I posted a similar post in the OS 10.12 forum and got no response. This problem seems to be internet mostly but I’m seeing other strange things, like external drives continuously going offline and back on. I’ve called Comcast for troubleshooting twice with a service guy coming over. Couldn’t find anything. Replaced the modem and some wires. I’m thinking of replacing the OS drive. It’s a 2TB that only has about 550GB available but I had to reclaim about 200. The internal drive is a spinning SATA. I’m thinking of replacing it with a 4 TB SSD. But before I spend $700 I want some educated guesses that this might be my problem. I’m not sure why the internet would be so slow to respond from bad sectors on a hard drive. Continually I can’t download a simple 15 MB file. Pages won’t open or take 10-15 MINUTES to open. Comcast speed test seems to be in the acceptable range except it takes about 20-40 seconds of sputtering before it even starts. Help!!!!! 2 MacPros 2009/2010 5,1 3.46 GHZ. 10.12.6.