Previous discussion here mentioned a workaround but no way to address the fundamental problem which is that the incorrect baseline scan is potentially used.
If there were a way to specify a specific commit for the sonar.pullrequest.base parameter and a potential timeout to wait for that result to become available then the entire system would be more robust.
With many hundreds of commits per day it is easy for the wrong baseline to get used. We frequently run into this problem of using a bad baseline.