Very slow performance with San Disk 3.2 Gen 1
I have a San Disk slim fit USB drive (USB 3.2 Gen 1). I've formatted it with APFS (encryption enabled). When copying a large file to the USB drive I see bursts of 20MB/sec, then it drops to 1 to 2MB/sec for about the same time. The USB drive is connected via an Apple USB-A to USB-C dongle. My Mac is an a M1 2020 Air.
Is this caused by the APFS encryption? The CPU doesn't appear to be doing much. I would have expected better and more consistent throughout.
MacBook Air 13″, macOS 13.2