Bought ticket 1/27 IND-SFO-TPE Premium Economy fare and applied for MUA

got my SFO-TPE (R class) cleared right after Christmas (1 month before! Christmas gift!) - but not the first leg IND-SFO (on the app it shows B class, UA 500)
have been curious why they are not cleared the same time… and want to know if I have chance to take a nap in the first class since the flight will be 7am in the morning (will be able to go to Polaris in SFO or other partner lounge for food later anyway)

no UA status only explorer card. *G from other FF program.

PS. my last experience using MUA on TPE-SFO-IND, my TPE-SFO route was cleared like 2-3 days before departure and then I was told to go to first by GA after I already sat in my 7A seat on SFO-IND flight thinking I was about to die from the long TSA wait… (there was a line at global entry… but no line general so I went there then got checked….. dumb me…)