Thanks for the reply Bob! It turns out that it was a context setting. I recently installed MODXStart (
https://modx.com/extras/package/modxstart) and the package creates site_start under the Web context. That's fine and all but when I went to view the context settings for the Web context, nothing was loading in the grid so I assumed that it didn't have any overriding settings.
I suspect that the grid didn't load—and this is me guessing—because I had to turn off compress_js. Ever since then, the manager has been working, but it's just a bit "finicky". I'll reload the manager page and the finickiness will be gone.
I know this is now off topic of the thread but I had to turn compress_js off because it was spiking my server CPU memory. I would hit 1GB of virtual memory and then the server would error 500 on me. I turned compress_js off and it stopped. Do you (or anyone) know why this would happen?