Suppose your JDL's write speed has become significantly slower than usual (e.g., only 20 MB/s).
In that case, try to download the SD Memory Card Formatter for Mac, developed by the SD Association, from the following link:
https://www.sdcard.org/downloads/formatter/sd-memory-card-formatter-for-mac-download/
Once the download and installation are complete, perform a low-level format on the JDL, and its write speed should return to normal.
Note: Low-level formatting will delete all files saved on the JDL, so back them up before the operation.