The Chupa to Yichud Room issue was discussed earlier. It is a completely separate issue, and has its own sources.
The Otzar Haposkim Siman 55:1:19 (v 16 p 83) – seems to be based (partially) on a Taz., and that was the minhog in Yerushalayim. See also “Edus Leyisroel” p 65 a discussion on this, and he brings sources that so was the minhog in Yerushalayim over 150 years ago.
The basic idea is either “kinyon” or hefsek (between chupa and the yichud). The idea is to “lead” to the yichud.
The Nitay Gavriel (chapter 37 footnote 1), brings a Taz, discussed by Shu”t Pri Hoadomo (??? ?????) v 3 p 10, a sefer “Takanas Uminhogei Yerushalayim”, Edus Yisroel, Shaar Hamifkad (??? ?????) Hil. Kiddushin p 16 who doesn’t give the reason as kinyon but gives a different reason (“?????? ???? ??????? ??????? ??? ???? ????? ?????? ???? ????? ??? ??? ????? ????? ??? ????? ?????, ???? ???? ???? ????? ?? ????, ??? ???? ?? ???? ?? ???? ???? ?? ???? ??????, ?????? ????? ?????? ?????? ???? ??????? ??????? ????? ?? ?????, ???? ?????? ????? ???? ???? ??????? ??? ????? ????? ????? ???? ????? ??? ?????, ?”? ???? ????? ???? ?? ???? ???? ???? ????? ??? ???? ???? ???’ ?? ??? ?????? ??????? ??, ?? ?? ??? ???? ???? ???? ???? ???? ???? ????? ????? ????, ???? ???? ?????? ??? ??????, ???? ????? ??? ????, ???? ???? ?? ????? ???”?). Klilas Chasanim (????? ?????) Siman 10:4, Shulchon Hoezer (???? ????) p 67, Divrei Chaim Dov p 24 brings a reason al pi Chassidus.