1817, it started as a stealth but was upgraded fully at some point by previous owner.
Both 3388 and 3369 + extra top tube I just got from CoV will take the UFS no problem. 1817 will not do it no matter what.
Threads in about half way and it's done.
Edit here is a picture. This is how far the
thread will go and then dead stop. No amount of vaseline or noalax will get this thread to move even another mm. There is no thread damage or anything like that. It's really odd. That top tube works with everything else just not the UFS.