This appears to be a failure to map the debugger. Do you have a folder %UserProfile%\vsdbg\vs2017u5 with files? If so I would recommend deleting it and restarting VS to force an update.

When opening the project in VS you should see output in the Container Tools window like:

Getting Docker containers ready...
C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe -NonInteractive -NoProfile -WindowStyle Hidden -ExecutionPolicy RemoteSigned -File "C:\Users\----\AppData\Local\Temp\GetVsDbg.ps1" -Version vs2017u5 -RuntimeID linux-x64 -InstallPath "C:\Users\----\vsdbg\vs2017u5"
Info: Using vsdbg version '17.12.11216.3'
Info: Using Runtime ID 'linux-x64'
Info: C:\Users\----\vsdbg\vs2017u5 exists, deleting.
Info: Successfully installed vsdbg at 'C:\Users\----\vsdbg\vs2017u5'