How to resolve persistent Time Machine errors and incorrect backup reminders on Mac?

How much free space do you have on your boot drive? If there's not enough for a local snapshot you'll get that notification.

Next, boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

After you erased the TM drive did you reformat it APFS?

This usually happens when Time Machine’s status gets out of sync, especially if you don’t keep the backup drive connected all the time. macOS keeps an old “failed backup” record even though new backups are successful, which causes the wrong reminders.

Removing the Time Machine disk, restarting the Mac, then adding the disk back usually fixes it. If not, deleting stuck local snapshots with tmutil in Terminal also helps.

Doc_Sandy wrote:

I have followed your excellent advice and have resolved the issue. Thank you!

That's good news.

How big is your boot drive? I try to maintain a minimum of 80-100 GB of free space at all times in order to facilitate optimal system and application performance.

Doc_Sandy wrote:

Sorry - forgot your first question. I have 13.5 GB free on my 250 GB HD.

That could be part of your problem. See if you can't clear up a minimum of 80-100 GB of free space to assure optimal system and application performance. I do it by getting an external SSD, formatting it APFS and copying my Pictures and Movies folders to it. Once I confirm my Photos and Music libraries work as expected on the EHD I delete the contents of the Pictures and Music folder on my boot drive. Do not delete the folders themselves.

If you're budget conscious I use the following configuration as it's the most economical to get a 1 TB external SSD:

This configuration is slower(500 Mbs read and write) than one with its own enclosure but I don't notice the difference since I can open a 170 GB Photos library in 1 second and a 350 Mb Photoshop file in 2 seconds or less.

Just some food for thought.

Doc_Sandy wrote:

Thank you. I understand. BUT ... this brings up a whole new problem. I have a 250 GB internal HD, but I only have about 15 GB of data on it. TM and my Carbon Copy Cloner Backup program only show themselves backing up about 15 GB of data. BUT ... I started checking the HD with Disk Utility and it shows several partitions, one of which is huge - taking up about 200 GB of space on the drive, and seemingly it is empty. So that leaves about 15 GB of data, and about 15 GB of free space. I have spent hours trying to figure out what is going on, and have contemplated erasing my entire hard drive and reinstalling the OS. Alternatively I have tried to figure out how I could identify what these various partitions are doing, and trying to fix the problem rather than using the nuclear option. I have also considered taking the whole **** thing to an Apple store and asked them to fix it for me. I do not have a lot of large files on this computer. I have a couple of dozen photographs, no videos, nothing that could explain this apparent problem of running out of hard drive space. I have contemplated posting my problem here for some help, and since people here seem to be so good, and so generous, I thought I might do that. It will take a few screenshots to show people what I am looking at. In any case thank you one again for your generous assistance.

Do you use Time Machine at all? If you do launch Disk Utility and check your boot volume to see if there are any local snapshots from Time Machine or from CCC. You can delete all of them except for the last one.

Did you try a Safe Boot and was there any change?

Sometimes it takes a while before the Mac can rescan the drive and update the storage situation.

Yes, there have been a number of images that are not showing. It's a glitch in the website management. I plan to notify them by posting here: Using the Community

Glad to hear it's finally settled down.