Custom map is blank after adding third node

[skldjfgskldjfgsklsjd]

I created a custom map and started adding nodes to it. It worked OK until I added a third node, then in View mode it’s just rendering as a blank white rectangle [not a very useful screenshot…]:

I removed the third node but it made no difference. The map renders fine in edit mode. I set the background to orange, but view mode is still white.
There are no errors in nginx access.log or librenms.log.
On the developer tools console we have:

Uncaught TypeError: Arrays are not supported by deepExtend
    selectiveNotDeepExtend http://venus/js/vis.min.js:25
    value http://venus/js/vis.min.js:42
    setOptions http://venus/js/vis.min.js:40
    o http://venus/js/vis.min.js:40
    createNetwork http://venus/maps/custom/1:783
    refreshMap http://venus/maps/custom/1:997
    interval http://venus/maps/custom/1:1029
    setInterval handler*Start http://venus/maps/custom/1:1026
    <anonymous> http://venus/maps/custom/1:1041
    jQuery 

Automatic maps work fine [well, show lots of nodes anyway].

[skldjfgskldjfgsklsjd]

The content of /maps/custom/1/data looks normal. No errors and contains data about all the nodes on the map.

[skldjfgskldjfgsklsjd]

I guess there has been a recent update around maps, judging by some other threads that were started recently. Unfortunately I had deleted the troublesome map, so I don’t know if the update will have made any difference to it. A manual map I have created recently has not gone in to the error state that my previous efforts did, so that’s promising.