[BUG] Set-PnPPageWebPart: Cannot set images for image / image gallery web part

^{Originally posted by robi26 August 30, 2021} Hi I'm trying to add and configure an image / image gallery web part to my pages using the following code:

$imgWebPart = Add-PnPPageWebPart -Page $page -DefaultWebPartType Image -Section 1 -Column 1
$json = $imgWebPart.PropertiesJson | ConvertFrom-Json
$json.siteId = $site.Id
$json.webId = $web.Id
$json.listId = $imageList.Id
$json.uniqueId = $images[0].id
Set-PnPPageWebPart -Page $page -Identity $imgWebPart.InstanceId.Guid -PropertiesJson $(ConvertTo-Json $json)

The $json looks as follows:

{
  "imageSourceType": 0,
  "imageSource": "",
  "captionText": "",
  "altText": "",
  "linkUrl": "",
  "overlayText": "",
  "fileName": "",
  "siteId": "139f5750-2d56-4783-8568-fad2668a1dd3",
  "webId": "1f25310d-b433-4153-b50f-4e9f4c19aaca",
  "listId": "3d17631e-2cdf-4584-a572-613cc8c5ccc5",
  "uniqueId": "9658870c-6a44-4f26-9bfe-33725bb5915a",
  "imgWidth": "",
  "imgHeight": ""
}

The web part is added to the page (shown when in edit-mode) but no image is displayed. Same when trying to add an image gallery. Even getting the PropertiesJson from a manually configured web part and re-setting it with set-pnppagewebpart does not work.

I also tried to set the imageSource property to the URL of the image. Doesn't help.

Expected behavior

Images are displayed.

Thanks for any help / ideas...