Wanted to provide an update with my 9.1.2 move. I too found the ISO upload bug. Download via url is the only way to get ISOs loaded at this time. Error shown:
starting file import from: /var/tmp/pveupload-93b7660434769d3896ec263ed8f3647c
TASK ERROR: failed to stat '/var/tmp/pveupload-93b7660434769d3896ec263ed8f3647c'
