I have had this issue for a while. I have a Surface 2in1 Go3, up to date on Windows Update an latest Quicken version.
The icon reflecting an attachment occasionally is not presented, but if you click the block it will show the attachment
It happens on both Cash and Credit accounts.
There was a bug reported and some blame Windows. Not sure I believe its a Windows.
I know its there, sometimes I forget and search out the attachment only to find it attached when i redo it.