I found this discussion after searching for what I have been experiencing in the past week or two.
I upgraded from a 13" M1 MacBook Pro to a 14" M3PRo Macbook - running Sonoma 14.3.1.
This behavior never happened on the Ma MacBook - only with the newer machine. Specifically, what is happening is that when I put the laptop to Sleep and return more than one hour later, I see multiple "warnings" to eject that SSD drive before disconnecting it. What makes it most peculiar to my mind is that it obviously reconnects that drive, and then boots it off, rinse and repeat. Every time I wake up the MacBook that external SSD is on the desktop as if nothing happened.
I actually have two external SSDs - the one that gets kicked off is simply external storage (for photos), but the other is my Time Machine designate and it has never been "kicked out" unceremoniously. Scratch that - it occurs to me that there have been occasions where the Time Machine SSD does not show on the desktop when I wake it up - but there was never the warning telling me to unmount it. And the only way I could get it to reappear on the desktop was to restart the machine altogether.
I did start seeing the Time Machine SSD getting kicked off even when I had the M1 MacBook (also running Sonoma), but that system never booted the normal external SSD.
Curiouser and curiouser.