Highcharts bug - label formatter function does not fire with multiple axis - highcharts

Question

I have a chart with multiple yAxis and I want to format each one differently. However, it seems with multiple yAxis, the label formatter function does not fire at all. Here's my options:
{
chart: {
backgroundColor: 'transparent',
pinchType: 'none',
height: 320,
events: {
load: (e) => {
}
}
},
plotOptions: {
line: {
states: {
hover: {
enabled: true
}
},
animation: {
duration: 750
}
},
series: {
lineWidth: 2,
}
},
series : [
{ name: 'charts',
type: 'line',
id: 0,
dataGrouping: {
groupPixelWidth: 8
},
},
{ name: 'marketcap',
type: 'line',
id: 1,
color: '#1fd3a3',
dataGrouping: {
groupPixelWidth: 8
},
},
{ name: 'volume',
type: 'area',
id: 2,
color: '#ddd',
lineWidth: 1,
dataGrouping: {
groupPixelWidth: 8
},
}
],
navigator: {
enabled: false
},
scrollbar: {
enabled: false
},
rangeSelector: {
enabled: false
},
// responsive: {
// rules: [{
// condition: {
// maxWidth: 500
// },
// }]
// },
xAxis: {
// crosshair: {
// width: 1,
// color: 'rgba(255,255,255,.5)'
// },
visible: true,
type: 'datetime'
},
yAxis: [
{
opposite: false,
gridLineWidth: 0,
minorGridLineWidth: 0,
height: '75%',
tickAmount: 5,
labels: {
formatter: () => {
// this does not fire
console.log('firing!!');
return this.value
}
}
},
{
opposite: true,
gridLineWidth: 0,
minorGridLineWidth: 0,
height: '75%',
tickAmount: 5
},
{
top: '75%',
height: '25%',
opposite: false,
gridLineWidth: 0,
minorGridLineWidth: 0,
visible: false,
},
],
tooltip: {
followPointer: true,
shared: true,
},
credits: { enabled: false }
}
Notice that I have 3 yAxis, and within each of those I have different keys and values. I need to have a custom format for each, but when I try to use the formatter function, nothing happens. Using the format string value works, but it does not allow me to format the string the way I want. Any ideas?