MacOS updated as of 10 Jul 2020, TT as of late March 2020. Had the same problem -- program would start, detect a pending update, and hang. I observed that the head processes in the execution stack was not consuming cpu cycles or storage bandwidth, or requesting network I/O. Stdsig's (SIG_HUP) resulted in the stack immediately exiting clean (exit=0) so I re-started it sandboxed (snitch, kvm, wireshark, audit) and found that it was completing what appeared to be a successful upstream connect, get, download, and (storage) write, but that the last storage I/O was closure of the download cachefile. It never moved the cachefile to a proper filename nor did it attempt to re-open (ie., the "hang" was the program sitting there with no active filehandle on the updated it just successfully downloaded). Looked like it has trouble either transitioning from the download phase or in starting the apply-update phase of the normal update cycle.
My fix: disconnect and isolate:
1. Stop TT (via 'quit' option of taskbar since TT would not open any window or activate any menus other than "Updating", which did nothing).
2. Set all network interfaces down and non-autostart on next boot.
3. Clean shutdown, poweroff (this is to prevent a shortcut that Linux and OSX can do on "reboot" depending on your bundle and age, a plain "reboot" is all Windows requires).
4. Poweron and boot normally. Verify no networking.
5. Start TT, it will complain about inability to connect upstream but will then let you proceed.
6. Main window should now come up. Re-enable networking and "check for updates" via TT menu as you would normally for a manual update check.
7. At this point TT behaved normally -- download to cachefile, move to tmpfile, re-open, apply, auto-restart, update installed on restart, main window opened after application of update as per normal ops.
8. Open previously saved tax file as normal, everything from here out gave no indication of any problem.
