As a last ditch effort I deleted all of the files and re-uploaded a second time and it did the trick. Go figure.
I am experiencing this same issue as of yesterday afternoon. I have made no php or add-on changes in the past couple of weeks now so this problem is completely out of the blue.
Speed testing shows an average 30 second time to first byte (TTFB). Yesterday I was getting constant timeouts and was unable to access the admin panel, but it’s marginally better today. I have tried not only disabling all of my add-ons but deleting them as well, but to no avail. Using the default theme also made no difference. GoDaddy tells me it’s not a problem on their end, and I suspect they’re right. My forums, using the same SQL database, run as quickly as ever.