How do you connect your Amiga to the TV e.g. Scart, VGA adapter etc?
This thread came to mind when I saw something similar on a TV the other day, not with an Amiga, but with a PowerMac I was trying to recover. My A1200 is connect to a TV via Scart, but the same set also has VGA and HDMI inputs and had connected the G5 to the VGA input. I noticed that sometimes the image was fine, and I could see the left hand side, after a power cycle on the Mac sometimes I'd lose the very left hand side, enough to lost the first three or four characters of the text output. My TV has a setting for pixel clock, and so by going in and choosing it (not even changing it) in the menus, and then exiting, I could see the whole image.
In summary, you might be able to fix it by altering a setting on your TV.