It's the slow spin up issue. Very common in Amiga's. Try upgrading to 3.1 (which I believe has a longer wait period) or replace your hard drive with a modern, faster one. CF and SD adapters (including ones that work in an A590) are dirt cheap.
True, some SCSI controllers have this issue with some drives, and some don't. The A590 was launched very early, and seems to insist on fast resetting drives, fast spin up drives. It's not only slow drives that can have the issue, some 10K drives take a little while to spin up to full speed.
Some much more modern PCs and laptops have a similar issue when booting from USB devices - will never boot from cold, only from warm, because the device is busy self checking when it should be booting.
It's probably a hardware hack to fix it on the controller, using a different drive would be an easier way around it.
