USB Hard Drives Not Recognised

I have a USB hard drive plugged into a Win10 laptop, that I'm accessing on a Win7 machine via a wireless network. It kept dropping out for a couple of seconds here or there, then went completely dead. Turns out it's an issue with the laptop, not with the network, because it doesn't show up locally either. I plugged it into all the available USB ports on my laptop and no dice, it wouldn't show up. Tried a different USB drive, same result. Tried the original USB drive in my Win7 machine and it works fine.

When I plug the drives into the Win10 laptop I can feel them spin up, but nothing shows up in My Computer or Disk Management.

It's a Lenovo...something or other. Not sure.

It does keep popping up a message saying it recommends I install a BIOS update, but when I click "OK" nothing happens.

I've got two USB hard drives and a USB mouse/keyboard all plugged into a USB splitter so they can share one of the laptop's USB-C ports because none of them are USB-C and why isn't USB3 a thing anymore FFS. I also intermittently have issues with the mouse/keyboard. But given that the hard drives also failed when plugged into the couple of USB3/US2 ports I do have, the splitter clearly isn't the issue here.

Both USB drives are externally powered, so that's not the issue here.

USB splitter may be the main problem.
Mouse don't require high speed port so connect it to a USB 2.0 port.
Connect the two USB HDDs also to a USB 2.0 port.

See if it works better.
With the USB HDDs connected to a USB 2.0 port, open disk manager (C:\Windows\System32\diskmgmt.msc). Does they show normally?

I tested plugging the drives into another port, without the splitter, and it still didn't work. The drives do spin up, but nothing shows up in Disk Management or My Computer.

Open device manager. Is there any yellow alerts of missing drivers?

Three of the ports have yellow exclamation marks, but they're not about missing drivers. They all say "port reset failed".

Try to uninstall the drivers on those that has Yellow alerts.
Right click and choose uninstall, then reboot.
How to Fix Unknown USB Device (Port Reset Failed) Issue for Windows 10 - Driver Easy

I've got them plugged into a laptop and then connected via network to a desktop. I keep getting errors when trying to copy about 20GB of files from the desktop to the laptop. I've had several attempts and it keeps failing at one stage or another, including most recently an I/O error which is what I was getting when the port reset failure happened.

Not sure if it's the network or the USB connection but something keeps failing. Drives are still fine at the moment so it seems to be an intermittent thing. I was getting the same the other day before they went offline completely and refused to come back at all.

- - - Updated - - -

Decided to take the network out of the equation and moved the files to a thumb drive, then inserted the thumb drive into the laptop so the file transfer was local. About halfway through, the drives all disconnected for about half a second and then reconnected.

Strangely, this only happened this one time. The drives never disconnect when they're not being used - I've been using the laptop a lot recently for watching streaming video online which has nothing to do with the hard drives and I've not had them drop out even once. But when I tried to do the file transfer, they dropped out.

Is it possible that it is the splitter, but after the splitter drops them they can't be recognised in any other port either? When they dropped out permanently last time I tried connecting them to other ports and got no result, so I assumed it couldn't be the splitter, but is it possible it just marks them as unrecognisable somehow until I reboot?