I’m not sure what you mean by synchronization.
can’t you do a drive test to troubleshoot the problem ?
or a A / Iur interface trace ?
because based on your few lines describing the problem I’d say you have a lot of preparatory work before we can start troubleshooting. for example:
qos stats : what do they say ?
on 2G side ?
on 3G side ?
For a problem on such a big scale, you can ask to the RNC’s vendor for support.