That's interesting. Struggling to suppress this error I had the exact same idea to replace that parameter with a global variable (initialized with a valid ID). I can say for certain that the global variable idea does not work within the context of the OnChange action of a combobox. I have even gone as far as doing both: attempting to trap the error with IfError and using a global variable:
ComboBox OnChange property
If(
IsEmpty(comboCEOselection),
false,
Set(
varIDTemp,
comboCEOselection.Selected.Id
);
IfError(
UpdateContext({conSelectedCEO: Office365Users.UserProfileV2(varIDTemp)}),
""
)
)
Still, every time this app is run the error is seen. It is so frustrating.

The detail of the error in Monitor show:
Office365Users.UserProfileV2 failed: The method 'UserProfileV2' has an invalid value for parameter 'id'
{
"status": null,
"duration": null,
"dataSource": null,
"responseSize": null,
"controlName": null,
"propertyName": null,
"nodeId": null,
"formulaData": {
"script": "",
"spanStart": null,
"spanEnd": null
},
"data": {
"errorContext": {
"entityName": "comboCEOselection",
"propertyName": "OnChange",
"nodeId": 14,
"id": 3441,
"diagnosticContext": {
"formula": "If(\n IsEmpty(comboCEOselection),\n false,\n Set(\n varIDTemp,\n comboCEOselection.Selected.Id\n );\n IfError(\n UpdateContext({conSelectedCEO: Office365Users.UserProfileV2(varIDTemp)}),\n \"\"\n )\n)",
"span": {
"start": 172,
"end": 211
}
}
},
"errorMessage": "Office365Users.UserProfileV2 failed: The method 'UserProfileV2' has an invalid value for parameter 'id'",
"raiseToastNotification": false,
"wasReported": false,
"error": {}
}
}
And:
Unhandled error
{
"status": null,
"duration": null,
"dataSource": null,
"responseSize": null,
"controlName": null,
"propertyName": null,
"nodeId": null,
"formulaData": {
"script": "",
"spanStart": null,
"spanEnd": null
},
"data": {
"errors": [
{
"Kind": 23,
"Message": "Office365Users.UserProfileV2 failed: The method 'UserProfileV2' has an invalid value for parameter 'id'",
"Source": "comboCEOselection.OnChange",
"Observed": "lblCEOselectionInfo.Text",
"Details": null
},
{
"Kind": 23,
"Message": "Office365Users.UserProfileV2 failed: The method 'UserProfileV2' has an invalid value for parameter 'id'",
"Source": "comboCEOselection.OnChange",
"Observed": "lblCEOselectionInfo.Text",
"Details": null
},
{
"Kind": 23,
"Message": "Office365Users.UserProfileV2 failed: The method 'UserProfileV2' has an invalid value for parameter 'id'",
"Source": "comboCEOselection.OnChange",
"Observed": "lblCEOselectionInfo.Text",
"Details": null
}
]
}
}