Tested on v1.12.12. The previous issue from #38 (comment) still persists.

Without addons to disable Blizzard's auto close, the Skyriding UI window will not show when clicking the button from within TTT.

Interestingly enough, the sound effect for opening and closing the window plays, but since TTT is located in the Options panel, and the Options panel cannot be force closed, the Skyriding UI will not show.

so the issue is, that the skyriding UI was being shown, but because I bypassed the panel system, it didn't get a location assigned to it. Since it didn't have any location of where to display the UI, it just didn't render the UI visuals (but sound effects etc were still playing indeed)
but now I tested it with 0 addons, so it should work this time 😛