Hello,
when you customize SharePoint forms with Power Apps, there's a little (or sometimes quite big) problem with the OOB code in SharePointForm1 Item property. Currently there's default code to get the first item of the SharePoint list if no item is selected:
"If(IsBlank(SharePointIntegration.Selected) || IsEmpty(SharePointIntegration.Selected),First('YourListName'),SharePointIntegration.Selected)"
I know this is made for the work in the Studio (documentation here), but this creates a problem if user has a slow connection. For example, if you have an approval flow attached to the item/form, approver clicks the hyperlink from the email to open the form and if he or she has a slow connection, it will show momentarily (maybe a second or two) the first list item's data and then it will load the correct item's data.
You can test this with browser's developer tools by setting throttling to Slow 3G.