USB-C Cable Not Working on 2017 iMac but Works on MBP

[sclough]

Long story short I'm trying to connect my Samsung T3 SSD to the iMac. I typically use it with my 2018 MBP. I got a new cable for it and cannot figure out why it's not working on the iMac. On the MBP I can use the cable and the drive works fine. When I use the cable on the iMac the drive does not work. Just for fun I took the USB-C charging cable for my MBP and connected it to the drive and the iMac and the iMac suddenly saw the drive.

So I'm confused. The cable is clearly marked thunderbolt and USB 3.1 Gen2 compatible. I think the T3 drive is a USB 3.1 Gen1 drive. However, the cable works fine with the MBP so I'm not sure why it wouldn't work with the iMac
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Not entirely sure the reason for this, but I flipped the drive upside down plugged the cable back in and now data works. Not sure why the cable won't work with the drive in any orientation, but I'm posting this here in case anyone else runs into a similar issue.

 

[Fishrrman]

Connect the t3 to the MacBook Pro.
Tell us what format the t3 is using.
Mac OS extended?
APFS?
Something else?

What OS is running on the old iMac?

 

[chabig]

I flipped the drive upside down plugged the cable back in and now data works.

There is no reason that flipping the cable over would make a difference. More likely the act of unplugging and replugging is what fixed it. Make sure the female ports are free of dirt/lint.

 

[sclough]

Connect the t3 to the MacBook Pro.
Tell us what format the t3 is using.
Mac OS extended?
APFS?
Something else?

What OS is running on the old iMac?

Both are on Catalina. The drive is APFS. No clue why it wasn't working but flipped the drive over plugged it back in and it worked.
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There is no reason that flipping the cable over would make a difference. More likely the act of unplugging and replugging is what fixed it. Make sure the female ports are free of dirt/lint.

It makes zero sense to me also. I plugged and unplugged a bunch of times and then flipped it over and all of a sudden it worked. Maybe there was something in it, but what's strange is it always worked with another cable and always worked with the MBP.

Regardless, since then it's worked fine. I set it as the startup disk and now the iMac is much, much faster and more usable.