I can't remember the exact phrasing, but are you talking about the error message that essentially says: "The Tardis is broken. Your backup has diverged into an entirely separate timeline, and I have no way of reconciling it. You may now sacrifice an entire weekend to do an initial backup again."?

I've been on a lucky streak for several years now, where I haven't gotten that one on any of my devices.

"Preparing backup..." taking an unreasonable amount of time is a regular occurrence, and some edge cases around adjusting TM backup size quotas aren't handled well. But other than that, TM has been working reasonably well for me to back up 10 TB over SMB to a Synology NAS.

My gripe is much more with Apple's abysmal support for SMB and NFS, especially after deprecating AFP. I've been back and forth between them over the years and over several OS versions, and their implementations for both are just terrible.

But over time SMB, for me, proved slightly more stable and performant, with the right tweaks in smb.conf, and authentication and permissions/ownership are easier to deal with than NFS, so I stuck with that.

I also yearn for the days where TM just worked, because somehow, the alternatives are even worse:

- Arq Backup does some things quite well, which is why I use it as part of my 3-2-1. But some of its bugs and implementation decisions just scream "hobby grade" to me.

- Kopia looks interesting, but it's not mature enough yet. Failed for me with absolutely cryptic error messages during repo init both times I tried it, with versions several months apart.

- Restic, Borg / Vorta: Not turnkey enough for me.