There are others who can't link too! Not just UT tickets.
I had an Premium Annual Pass (PAP) and in May I had to go to the Odysey Building and exchange it for a new RF Green PAP. I did so, now only to find out that those exchange PAP can not be linked to MDE, or even affiliated with my account. Now if you had bought a new Green PAP after it started, like my daughter and her family, those could be linked to the MDE, but not the exchange ones. I called IT and was told there was an issue linking the exchange PAP.
So I purchased my ticket from Disney and I can't link mine either. However, my DH is using a voucher to get a new PAP next month and I could link his voucher. Because of this I can reserve FP+ for him and was told that
after I checkin and they manually link my PAP, I can be copied to his FP+. I did check on the "copied to another person" in manage FP+ and it was an easy process.