`TypeError: n.data.map is not a function` error on graph

[AlistairFielden]

When accessing the web page for the server sometimes the chart object shows 'TypeError: n.data.map is not a function'. See attached screen grab. Clicking the refresh icon for the chart shortly after will usually have the issue remain. Wait a few seconds and click the refresh icon the chart then populates.

This seems to be worse on my home system which has 8 clients connected all but one of which is included in the chart (so 8 chart pens in total (1 server & 7 clients). The other 2 systems I've set up both with a single client connected to a server only very occasionally give this issue.

With error

After refresh a couple of times