[SalesForce] SFDX: Tests do not run in Visual Studio Code

I am relatively new to SFDX and have the most recent updates for both VSCode and Salesforce CLI.

I am unable to run any Apex tests on a sandbox using the UI in Visual Studio Code. When doing so I get the following output

sfdx force:apex:test:run --tests Plan_XXXX_ControllerExt_Test.testxxxxController --resultformat human --outputdir c:\Users\xxxxxx\Documents\xxx\xxxxx\.sfdx\tools\testresults\apex --loglevel error
ERROR: Unable to invoke async test job: Cannot read property '1' of null.

When running that directly from the CLI I get the following

WARNING: In salesforcedx v41 and earlier, the --resultformat parameter caused the apex:test:run command to wait for test results rather than finishing immediately and returning a test run ID. In salesforcedx v42 and later, the --resultformat parameter will no longer cause the command to wait. To wait for test results, include the --wait parameter.
ERROR: Unable to invoke async test job: Cannot read property '1' of null.

However, if I run the tests without the –resultformat tag through the CLI I am able to get back test results.

e.g. –

sfdx force:apex:test:run --tests Plan_XXXXX_ControllerExt_Test.testxxxxController --outputdir c:\Users\xxxxxx\Documents\xxx\xxxxx\.sfdx\tools\testresults\apex