IMAC 24 - very slow transfer speeds on Sandisk Extreme Pro V2 1TB SSD drive

How is the drive formatted?

Your Sandisk is not an Apple product, please contact the developers of the product. However before doing so please execute a Safe Mode restart with all external peripherals disconnected and then restart normally and retest.

Use Safe Mode to isolate issues with your Mac

Okay, lets look to see if there is something installed on the Mac that is causing the issue. For example if you have any third party antivirus, cleaning or any other maintenance apps that can cause major issues.

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again.

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click https://discussions.apple.com/docs/DOC-250000211

Just reformat it and it should be fine.

Thanks for the Time Machine info, it must have been disconnected when you ran your EtreCheck report as it did not show up.

Well, you may have gotten a bad one. By the way, I only recommend using OWC enclosures as they specialize in Macs, have great support and their prices are very reasonable. Also, it isn't just me, you will find many experienced users prefer OWC products.

You may want to consider returning the Sandisk and visiting Macsales.com, they have many external SSD's, I'm sure you will find something that suits your needs just fine. Something like a:

OWC Envoy Pro EX Thunderbolt 3

I don't see any of the normal issues and your iMac otherwise appears to be operating just fine. I'm not sure if you got the Sandisk to use as your Time Machine backup. The reason I bring this up, is it appears you are not backing up the computer. If that is correct please being using Time Machine ASAP to safeguard your data. Operating any computer without a sound backup plan is shortsighted and a guarantee of losing data at some point. Please refer to Back up your Mac with Time Machine.

Another option is to return the Sandisk and get another one in exchange and test the new one. If it works that simply proves that you may have purchased a defective one. If the problem persists then it could be a compatibility issue. In that case you can try another solution.

If you want to persist with the Sandisk then I would recommend contacting AppleCare and Sandisk for support as I'm out of ideas.

I saw that you did not like the pricing for the first OWC solution I offered. Another is the:

OWC Mercury On-The-Go Pro: Get Maximum Storage Within Minimum Space (macsales.com) and a

5V 2.0Amp Barrel Style AC Power Adapter for OWC Mercury On-The-Go (macsales.com)

Finally as you are in the UK, you can use an OWC UK vendor. To locate one please use High-Performance Workflow Solutions - OWC Digital

You will need a USB adapter which you can find at Amazon for about $10.