Thanks for the additional information.
Yes removing the connectionId from the connection “worked” for you because it actually broke the binding 
You asked before:
does SonarLint support a proxy?
Is your SonarQube Server behind a proxy? Currently, SonarLint does not support this out-of-the-box, but maybe you could give either this or this a try In order to pass proxy configuration to the SonarLint Language Server (java backend).
Trying it on your machine first (not a DevContainer) could give you higher chances of success 
Looking forward to hearing the update,
Sophio