The first problem could be from a variety of sources really. There could be delay in the equipment you are using, you could be hearing acoustic reverbs interfering with what you are hearing.

Second problem there are a few ways to deal with it. Either you can match the hi's up or just crank the bass gain up to max until you can hear it when you are cueing before returning it to normal levels before you start your transition. You have to be aware that some basslines when beatmatched can cancel each other out which could be a source of this problem.


If you want a bit more detailed help fro people it might be a good idea to actually state what sort of equipment you are using so that if they have any opinions based on specific equipment or known problems they can chip in.