Apologies for the late reply here everyone.
This does appear to be the same Chromium issue happening as linked above (https://issues.chromium.org/issues/369633257).
This means that the issue is related to the underlying Chomium engine and will need to be fixed by that team. It is not related to changes made in Brave, nor does it have anything to do with the number of items present in the context menu. The issue is labeled as P2 so I imagine this will be fixed sooner rather than later.
One way to test and see if the issue is pushed in later Chromium builds would be to download the Brave Beta or Nightly builds and see if the right-click context menu issue is still present in those builds.