I ran into this issue today and the solution of creating the 1:1 sequence and then copying and pasting my elements into it did not work (for Premiere Pro 2022, build 22.5.0). I noticed that in the ‘Transform’ drill down (below the Text layers), the Scale had been adjusted from 100 to 56. Resetting that to 100 gave me the same size titles as I had in my 16:9 sequence. Hope this helps someone — what a frustrating issue!