thanks but unfortunately no - the two USB 3.0 ports of the RPi4 do not work with the SSD (although it has a USB 3.0 port itself), but I moved from one USB 2.0 to just the other USB 2.0. port. So it is a difference between the two USB 2.0 ports... I know, super weird.
That strange indeed. At the RPi's the USB ports current limit is for total current (around 1.2A), theoretically no individual port current limit. I think your SSD need power that these ports barely can provide. Looks like one of the USB2 port can handle it for now, but the question how long and how stable.
Two thing:
I think in the config.txt can be activated the high current output adding the line "max_usb_current = 1" (you should have a proper power source for RPi).
You can use an external powered USB-HUB connected whichever RPi USB port (the SSD will be powered by HUB).