Sanghamitra SF is a train that requires extensive maintenance from SWR. The train is always overloaded and absolutely abused by all passengers, most of whom are labourers who want to go to Bengaluru come what may.
It is generally very clean when it starts from SMVB, but is almost unidentifiable when it comes back ЁЯШВ
So sick coach replacement is very much plausible....
more... Probably SMVB doesn't have as many reserve coaches as SBC, so it takes time for replacement.