To be clear, I can download images if I turn the USB bandwidth down to the minimum for my camera (ASI094 MC Pro). It just takes twice as long to download as it does with the SD card & the bandwidth turned all the way up. My images are 72 MB each.
Without turning the USB bandwidth all the way down, I can't even download a single image, so adding a delay between exposures won't help me.
This is for a fresh install of Kstars 3.4.3 on Raspbian booted from SSD. I don't have this problem running the exact same image off the SD card. I'm not downloading files to the laptop, just using a laptop to control the Pi4/4GB remotely via NoMachine (faster/smoother than VNC) over my home WiFi network.
I'm not using a USB hub. Thanks for suggesting this. I will try that too. Have had no trouble at all booting from the SSD. No under voltage warnings on the Pi4. Powered using a 5v 3.5A CanaKit AC adapter that came with my Pi4.
Boot time from the SSD is around half what it is booting from the SD card. I had to completely remove the SD card from other Pi to make it boot from the SSD. It's trivially easy to copy the SD card image over to an SSD and then boot from the SSD instead:
www.tomshardware.com/how-to/boot-raspberry-pi-4-usb
For the present, I plan to run with the bandwidth turned to minimum (about 6 seconds to download an image from the camera compared to 3 sec to SD card).