Multiseries charts stopped working in version 3.17

[Multiseries charts stopped working in version 3.17]

Our multi series charts are not working in versions 3.17 and 3.18. With the only change being a Fusion Chart upgrade, all multiseries charts error out with the following:

core.js:6498 ERROR TypeError: Cannot read properties of null (reading 'showplotborder')
    at t.a.parsePlotAttributes (fusioncharts.js:30:250186)
    at t.a.allocatePosition (fusioncharts.js:30:254484)
    at t.prepareAttributes (fusioncharts.js:13:200599)
    at c (fusioncharts.js:13:198928)
    at f (fusioncharts.js:13:199127)
    at t._mapChildren (fusioncharts.js:13:205523)
    at t.prepareAttributes (fusioncharts.js:13:200623)
    at c (fusioncharts.js:13:198928)
    at f (fusioncharts.js:13:199127)
    at t._mapChildren (fusioncharts.js:13:205523)

Change the version back to 3.16 and all is well.

Please point us to something that describes what we would need to do to make multi series charts work in later versions. Clearly something has changed, we just need to know what it is.

Thanks!

[How do you format the tooltip on the sum column in a waterfall chart?]

On a waterfall chart we can control the formatting of tooltips. For example, an item is configured like this (in TypeScript):

{
  label: label,
   value: value,
   toolText: `${fmt.format(value)}`
 }

However, this does not work for a sum column. How can I achieve the above (custom formatting) of a value in the tooltip on a sum column?