HP G255 G7 sd slot won't read exFAT cards

[NigelSS]

I've a new HP G255 G7  notebook that I'm pretty pleased with,  but have recently encountered a problem with. It came with Win10 64bit pre-loaded. It's had a few Windows updates since then and is pretty much fully up-to-date. I can see no installed updates relating to the SD slot, though I don't really know where to check for such details in the updates that have been applied.

So here's the problem :  I've got some 64gb sdxc cards that I use in my camera. Whilst I'm aware that the built-in SD slot on the notebook isn't very fast, when I try and use it on the exFAT formatted 64GB cards,  the notebook starts Windows Explorer on the drive, then hangs, becoming almost completely unresponsive until I remove the card. At best,  a file copy from the card shows it reading at a few kb/second.  I've no problems with FAT32 formatted cards. Given that the SDXC format has been around for years now and the notebook is new,  I'm really surprised by this and of course would prefer a solution - possibly there's a different driver I could use, though if I try and update the driver I'm told that the one currently installed is the most up to date.

The exFAT card works fine via a USB 3.0 multi-card reader, and a 32GB card that works fine in the SD slot in FAT format displays the same problems when formatted in exFAT as the 64GB card, so its not the cards that are at fault.

The User Guide for the 255 G7 makes no mention of the SD card slot, so I don't know of any limitations it might have.

The device driver appears to be provided by Alcorlink Corp, 17/04/2018 rev 2.0.148.24503, and shows AmRdclco.icl and AmUStor.sys, both diginally signed.

Update : I've also installed a new Alcorlink driver, 2.0.149.100100, but that hasn't resolved the problem.

Anyone got any ideas?