The delay in mass production and export of j-10b is connected with development of chinese ws-10 engine.
The PLAAF currently doesnt use ws-10 engine in any if their main aircrafts,as none can accomodate ws-10,. Only j-10b can be fitted with ws-10 engine.
The previous engine manufacturing facility was having priblems in mass producing ws-10 engines,so the production was recently moved to new location in guangzou.
Same fascility will produce the ws-15 engine for chinese top dog the J-20.
We have seen recent videos of j-10b being tested with new enginr,alongside j-20 . PLAAF is comfortably using j-10a and in no urgency to replace them,so dont need to rush the mass production of ws-10 engine.
It is plausible that mass production of ws-10 is tied with whenever ws-15 engine matures and is certified for use in j-20,and we may see j-10b and j-20 entering final production together,and that may be a few years away.