YONO is pretty bad and I used them too because SBI as my first bank account like most of the Indian residents and 6/10 times the payments will be failed due to server error and for a government bank with such large userbase not given proper resource like HDFC or ICICI do.
As far as information from SBI employees go, they paid a lot of money to TCS to develop this app and look at what sort of a app they ended up with. From the outside it looks good but inside its buggy and not adopted to modern smartphones. Often goes on maintenance over weekends and server crashes are nothing new.
Indian government needs to hire quality developers as in the one hired by Paytm, Jupiter, DBS and such. All of government apps and banking apps (Except DBS) I have come across outright suck that I'd rather prefer to use their services through third party apps.
TCS is infamous for making petty apps, yet companies keep delegating development tasks to them.