I hope this finds everyone sane, I nearly lost my mind trying to resolve this issue. I was able to fix it by going to:
and downloading and running the Opta Factory Reset tool:
https://opta.findernet.com/download/OPTA%20Arduino%20Factory%20Reset_1.0.0_x64-setup.exe
Then downloading Arduino PLC IDE 1.0.85 from:
https://opta.findernet.com/download/Arduino-PLC-IDE-Installer_1.0.8_Windows_64bit.exe
I am not sure where the underlying issue was, but this resolved 4 days of beating my head against my keyboard. Good luck!