I am getting tons of (about a hundred) “Disk Not Ejected Properly” notifications/messages for two external hard drives (one drive has one partition, the other has two partitions). I'm running Mojave 10.14.4. I never had these issues when these two drives were connected to a MacBook also running 10.14.4. But, now I have them connected to an iMac and these messages have been displaying recently the past day. Had not happened for about a week's worth of use prior to yesterday. The disks still seem to be working fine but for some reason it's worrisome to me.
Both drives are connected via Thunderbolt 3. Under the "Energy Saver" preference pane, I have "Put hard disks to sleep when possible" and "Enable Power Nap" checked.