I don't know if it is a related issue but I also couldn't upload a file Octoprint with the plugin. Octoprint Plugin option missing after I sliced I only had the option to "save file". Figured it must have had something to do with me reflashing octopi. Couldn't find Octoprint connection option under "Manage printer" in Cura. So I uninstalled plugin and tried again twice without luck.
using:
Cura 4.8.0 on WIndows 10
octopi 0.18.0
octoprint 1.5.3