I have found a possible bug in the risk module of the BigPicture.
My organisation uses a custom risk matrix.
To align the risk categories to the organisation I created 2 new custom fields as select list (single choice) and configured the risk module to use these fields for probability and consequence.
I can then edit the jira issue to use these two fields to categorise the risks.
What works
The risk matrix updates with my categories on the x and y axis.
The risks (issues) with the fields updated by editing the issue fields appear correctly in the risk matrix at the intersection of the relevant probability and consequence.
What doesn't work
When I drag and drop a risk in the risk matrix the custom fields aren't updated and the following error is visible when I refresh the risk matrix.

Reloading the risk matrix will display with the risk(issue) in its dropped location, but the error will remain and the custom fields haven't updated.
Running fix integrity checker errors reverts the risk(issue) to it's previous state/location on the risk matrix.