Hey @Anonymous ,
I have had issues with this before also, I believe its because SharePoint gets this data from the hidden SharePoint Users Table and in my experience, the picture has some trouble. In my experience, I have found using the Office365Users connector to be much more reliable, if a little slower.
If you find and load the Office 365 Users Connector, you should be able to change the Image field to this:
If(IsBlank(ThisItem.Employee.Picture); Office365Users.UserPhotoV2(ThisItem.Employee.Email); ThisItem.Employee.Picture)
(I'm in the UK, and I think in some countries / tenants the connector is called Microsoft365Users...)
It can be a little slower to get the images, but they should work a lot more reliably (sort of!)
If that doesn't work for you, you can also try loading the data into a Collection first, you will need an actionable item, like a button, but it sort of "loads" the data directly into the app, making it locally available, then just set the gallery data source to be the collection...

This may or may not make it do the behind the scenes sync!
Good Luck!
Rob