Altium: "Net [] contains floating input pins", but they seem to be connected
My first guess would be that this has to do with the REPEAT statement. Have you tried reversing the indices?

Anyways, after also having lots of troubles (especially there not being a 0 index) I have stayed away from the REPEAT statement. Instead, I decided to simply place multiple instances of the sheet symbol (not copies of the sheet). This also allows more fine-grained control over which net goes into which instance instead of relying on indices. I highly recommend this approach even if it means you'll need a little more space in the schematic.