I’ve lost track of all the info you gave on the drive. But, I kept a sticky note of things to check.
1) Check if the USB is version 3. Version 2 is quite a bit slower than 3. Also, most people think they can plug a USB 3 into any USB port and it will still be a 3. Not true because the slowest wins. If you plug a USB 3 into a USB 2 port, it becomes a USB 2 drive. Vice versa is also true. A 2 drive into a 3 port runs at USB 2 speed. To get full USB 3, both the drive and the port must be USB 3.
2) Fill status of the drive. If the drive is close to being full, it may be having to swap data a lot. That can really slow down any application. You wouldn’t notice it on your regular applications because they would run off the regular drive. However, you would notice it on anything else that ran from the portable drive. I recommend less that 85% full, but others here are more tech savy than myself.
3) Drive death immenent. I don’t know what it is like to have a solid state drive die. But, on a traditional spinning drive, the drive will mark sectors as bad when the drive has trouble accessing them. This can result in corruptions. And, as the drive has to work twice as hard to find all the pieces it keeps moving, this can cause slower run time. Thus, you get slower and slower and more frequent data corruptions in an application. I don’t remember how, but you can test for this.
Thank you Adriani Botez for reminding me of the 2 versus 3 issue. I lost track of who suggested the other two…
Good luck and let us know the results,