I have the same issue: I enable startup programs in Settings, Apps, Startup, such as Backblaze backup, APC UPS Powerchute, and TeamViewer.
Upon restart of computer, all are set back to not Starting. Since there are 3 programs that this is happening to, I would have to assume it is Avast One (Paid Family version).
I have reinstalled Backblaze, and Team Viewer with no avail.
They are not blocked in the Avast Firewall. Windows 10. I have another Windows 10 machine- they all work fine on startup.
Any suggestions?