Old portable HDD just went from USB 3.0 to USB 2 speed

I have an old Western Digital My Passport 2TB USB 3.0 drive (HDD). I don't recall ever running a performance test on it, but in the past transfer speeds seemed "reasonable". Today a backup to the drive seemed very slow. I ran a speed check - using the ATTO Disk Benchmark tool - and saw that the drive was running at USB 2.0 speed. just to be sure I tried the benchmark on 2 computes and 3 USB 3.0 ports. Same results on all. And I tried with 2 USB 3 cables. And to be further sure, I ran the benchmarks against another device in each of the 3 ports. All 3 ports were capable of close to USB 3.0 speeds.

Is there anything that could cause a (previously) USB 3.0 device to suddenly slow down to USB2 speed? I don't remember when I got the device but I'd guess 6 or 7 years ago. I know there are things that can kill HDDs but can something just slow them down? Could this be a sign that the device is dying?

Edit: Corrected device size. It's 2TB instead of my originally stated 3TB.

With electronics one never knows for sure how long they will last. I've had a few die, both NAS drives and external USB drives. In checking further turned out the interface in the drive case had failed, not the drives themselves. I was able to salvage the drive, last one was a 2TB NAS drive that is now quite happy as an internal drive in my Win11 Desktop from April.

Yes, I have had drives drop read/write speed. In fact, I'm using one right now. In my case, it's as @Berton said. It proved to be the little logic board inside the enclosure that converts the sata connection of the drive to usb. Some enclosures make it difficult to get inside them. If you can do so, you can buy another enclosure to install the drive into for about $20. However, external drives have really come down in price and your drive is at least 6 years old, so purchasing a new drive might make more sense.

Thank you for your replies. I will almost certainly buy a new drive. Now all I have to do is decide whether to stay with an HDD or splurge get an SSD. The only time I use the portable drive is when I want to take a quick backup on a laptop or when I need to move large files between computers. If I don't care about speed I can (usually) use a NAS.

Is an ssd better. For sure. But you have to weigh cost+amount of storage your get for your buck against how and how often you use an external drive. As an example a 1tb ssd is $100-$130, double that for 2tb. A 1tb HDD is $50 or you can double it to 2tb for $62. If an external drive is used a lot every day, you would definitely want an ssd for all that is good and wonderful about an ssd drive. For data transfer and occasional backups that you can set to run when you go to bed, a hdd works just fine.