More external SSD problems: "Disk not ejected properly" when it's already ejected.

If you are getting repeated notifications, then I suspect macOS is sensing the SSD has been reconnected which means something in that chain of devices is making it appear the SSD has be reconnected. It could be any device, adapter, cable, or maybe even the drive itself, or maybe the port on the laptop if the port is faulty.

If the SSD is connected directly to the Mac and you still have this problem, then most likely it is something to do with the drive itself or its cable, or the USB-C port on the laptop, although you still cannot completely rule out any other connected device from causing a problem. Try disconnecting all other external devices and testing the SSD by itself when connected directly to the laptop...try it on each laptop port as well.

Are you "ejecting" the SSD or just "unmounting" the SSD. There is a huge difference. If you are using the little arrow next to the mounted volume or dragging the volume to the Trash, then you are actually "ejecting" the SSD which first unmounts the volume followed by a "disconnect" of the SSD perhaps even powering it off...the only way to get macOS to physically an ejected drive is by physically disconnecting the drive and reconnecting it.

"Unmounting" the drive can be done in Disk Utility...where "unmounting" a volume will still leave the physical drive detected by macOS where macOS can communicate with the drive so it is possible to re-mount the volume without having to physically disconnect & reconnect the drive.

I'm guessing that you are actually "ejecting" the drive whereby the Mac is no longer able to communicate with the physical drive. In this case the drive must be physically disconnected & reconnected before a volume on the drive can be mounted again.

If, however, you eject the drive and you physically disconnect the SSD and you receive an "Disk not ejected properly" notification, then it just means that macOS did not have time to fully unmount the volume(s) located on that drive before you disconnected the cable from the laptop. I miss the days when macOS actually notified the user when it was safe to physically disconnect the drive from the Mac.

The first page of that linked thread shows drives disconnecting on their own, then reconnecting. Your issue is a bit different....you are already manually "ejecting" the drive yourself and receiving the notifications afterwards. The posts on the first page of that linked thread are reporting that their external drives are disconnecting on their own, then reconnecting on their own. Perhaps they are related...there is a bit of similarity, but yours is the first time I've seen the issue occur after someone has ejected a drive, but left it connected. If it is a macOS issue, hopefully one of the next updates will resolve the issue, but it usually takes time for Apple to push out updates....assuming Apple is even aware of an issue.

Like I said before, the best way to confirm the issue is related to just that single drive is to disconnect all other external devices to see if it still happens to that drive. If it happens to that drive, then there is some sort of issue with that drive...perhaps a hardware issue (drive or computer), or perhaps some sort of compatibility issue. Unfortunately at this time there are not enough specific details from any of the reported cases to determine if a particular USB3 or Thunderbolt chipset is involved, or whether this is a more generic issue affecting multiple chipsets. Perhaps another drive from another brand will perform as expected (especially one utilizing a different USB3 or Thunderbolt chipset). As of now, it is just a crap shoot on what drive to try next since people have not provided enough details in any thread to help us provide an educated guess on a good drive to recommend trying next.

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