Custom Sensor not showing a value

Same sensor from before (https://kb.paessler.com/en/topic/86773-script-returning-a-string-value) but I'm having trouble getting my time elapsed sensor to actually display the value I'm passing to it.

$module = (Join-Path $(Split-Path $env:SMS_ADMIN_UI_PATH) ConfigurationManager.psd1)

Import-module $module

$SiteCode = Get-PSDrive -PSProvider CMSITE
Set-Location -Path "$($SiteCode.Name):\"

$syncResult = get-cmsoftwareupdatesyncstatus

$timestamp = get-date
$timeDiff = $timestamp - $syncResult.lastSuccessfulSyncTime

$xmlOutput = '<?xml version="1.0" encoding="UTF-8" ?><prtg>'

$xmlOutput = $xmlOutput + "<result>
<channel>Sync Code</channel>
<value>" + $syncResult.lastSyncErrorCode + "</value>
<unit>Absolute</unit>
<limitmode>1</limitmode>
<LimitMaxError>0</LimitMaxError>
<LimitErrorMsg>SCCM Error: Sync with Microsoft Update Catalog failed.  Code: " + $syncResult.lastSyncErrorCode + "</LimitErrorMsg>
</result>
<result>
<channel>Successful Sync Age</channel>
<value>" + $timeDiff.TotalHours + "</value>
<unit>TimeHours</unit>
<float>1</float>
<DecimalMode>All</DecimalMode>
<limitMode>1</limitMode>
<limitMaxError>170</limitMaxError>
<LimitErrorMsg>SCCM has not been able to sync with Microsoft update in 7 days.</LimitErrorMsg>
</result>
"

$xmlOutput = $xmlOutput + "</prtg>"
$xmlOutput

When I tweak the channel settings, they are reflected in PRTG (converting the channel to TimeHours, for example). However the value is always zero. If I run the script manually in Powershell the totalHours property seems to be correctly displayed within the 'value' tag.

channel-configuration channel-settings custom-sensor powershell sccm