Weird USB behaviour on RazPi 4

This seems strictly a hardware problem on my 4G RazPi 4.
AFAIK, the (blue) USB3 sockets have a 500mA current Limit, and the (black) USB-2 sockets have a 250mA limit. Please correct if you know better.

I'd been running on sdcards, but it was SSD time. My setup had been

• Ralink RT-530 external wifi in usb3
• Micro SDCard in sdcard -->usb converter in usb3
• Logitech wireless mouse/keyboard adapter in usb-2

and it all worked fine. The internal sdcard slot was vacant. So I unplugged the sdcard converter and plugged in the (kingston) SSD. That's when the trouble started. It came up, with no mouse. The keyboard was sort of OK, but the mouse was gone, and both were on the same adapter. I'll spare you the blow-by blow, but trying the devices around gave me only one working combination.

• Logitech wifi keyboard/mouse adapter in usb3
• ssd and external wifi in usb2

Replacing the battery in the mouse brought no joy either. Still no mouse.

The RazPi is behind a tv on a small table. I have another larger table with keyboard & mouse, so wired is not an option. The switch that brought this about was pulling the sdcard usb converter, and inserting the ssd with it's little case. I did have a faulty ssd case before, which stopped play for a while. So the case is a component in the chain, with it's own pcb & ICs.

What's even more irritating is that I'd class myself as a hardware guru, and know enough to know this doesn't make much sense. I'd already done an rsync successfully on my pc. Why?:banghead: