The Ctrl + Tab and Ctrl + Shift + Tab are common shortcuts for cycling tabs in other file manager and browsers, so it would be useful to have these shortcuts also in Thunar.
I was checking ~/.config/Thunar/accels.scm and see that we do have shortcuts assigned for it, but they aren't active.
I was using Alt + 1 and Alt + 2 to switch between tabs yesterday, as those are the shortcuts I used sometimes in mousepad. I see that Ctrl + Tab and Ctrl + Shift + Tab cycle through the toolbar controls.
Can confirm <>Primary>Tab BackTab ISO_Left_Tab Don't Work, sounds like a bug but not in Thunar I don't think, though thats total guess work on my part (at this point)