CC won't connect to Calibre

[HelenaF]

I'm trying to update the CC library on my ereader to match the current calibre library on my computer. (I want to send one new ebook to CC and update the metadata for a couple other books.)

I cannot establish a functional connection between CC and calibre to do this, either through wireless connection, content server, or a usb cable.

Devices

• I am using a 2015 MacBook Pro running OS X El Capitan 10.11.6.
• I am running calibre version 2.71.0
• The device running CC is an Onyx Boox Note2
• My WiFi has been a little slow but otherwise fully functional; I'm able to browse the internet easily on both my computer and my Boox, so I don't think the WiFi is the source of the problem.

I have previously had success connecting calibre to CC between these two devices via both wireless connection and the content server. Yesterday and today I have been unable to do so.


Wireless Connection
When I try to sync via wireless device connection I get a message saying "Could not find calibre. Have you started "wireless device connections" in calibre?"
I have started wireless device connections in calibre. I tried turning wireless connection off and then on again; I tried shutting down calibre and restarting it and shutting down my Boox and restarting CC; I switched WiFi networks. Nothing worked.
I manually re-entered my computer's IP address and the fixed port number into CC, and triple-checked that they were correct. Still I got the same "Could not find calibre" message.


Content Server
Basically the same as above. I get a message saying "Cannot find Content Server." I have turned everything off and on again, and I've manually entered the IP address and port number, and nothing works.

USB cable
This one is a little wierder.
I tried connecting my Boox to my computer using a USB cable. Calibre did recognize my device this time. But there were two issues:
1. Several books in my calibre library did not say they were on the device (as in, the "on device" column where the rest of the books said "MAIN" and had a green checkmark was empty for these books), even though they definitely are on my CC library on my Boox.
2. I could not get any books to send to my CC library. I clicked "send to device" and got a notification from calibre that the book was sent to my Note2. And the calibre library showed that the book was now on my device, with the word "MAIN" and the green checkmark in the "device" column. But the book is not actually on the device! I can't find it anywhere in my CC library including if I sort by date (calibre), where it should show up on top as the most recently added book.

If anyone has ideas about what I can do to get my libraries to sync I'll deeply appreciate it!