Sandisk Extreme Pro UHS-ii USB-C SD Card Reader Issue (SDDR-409)

Can someone please help me with an issue I’m having with my Sandisk Extreme Pro UHS-ii USB-C card reader (SDDR-409)?

During a copy operation, the card reader reads for a little while (LED flashes on reader) but then stops reading for a long time (no LED flashing) and eventually starts reading again. The copy process is extremely slow.

I’ve tried resetting SMC & NVRAM which didn’t fix it. It’s writing to a MacBook Pro (15-inch, 2019) with a fast SSD so this isn’t the bottleneck.

This is the 2nd reader (same model) I’ve got which has this issue. I bought another one after my initial one failed and thought it might have been an issue with the reader but my brand new one also has this issue.

Here’s a video of the issue showing a comparison to a cheap USB-C card reader: https://youtu.be/WZk2VLjyM8A

Edit: I also tested this card reader on my wife’s Macbook Air and it has the same issue.