EVA can take some time to update prices after you dock at a station. There are two reasons for this, one of which is easily fixed and partly helps to fix the other.

The first problem is finding out that you've docked. Remember that EVA gets no realtime data from Elite:Dangerous itself, it relies on getting information from Frontier's servers and it has to ask for it. You can set EVA to check automatically every 30 seconds but no more often than that, to avoid overloading Frontier. This can be one source of delay.

This sounds as though it would be easily fixed by installing and running EDProxy on your PC or Mac. This gives immediate notification whenever you enter a new star system. Unfortunately it doesn't give notification when you dock, although there may be options in the future to help that.

In the meantime, the workaround is very easy; all you need to do is tap the "Refresh" button soon after you dock.

The second problem is that even after you do this, sometimes the prices don't update immediately. The issue here is that sometimes Frontier's servers are a little way behind the current state of the game. In fact, sometimes the information reported by Frontier actually goes backwards to a previous system! EVA filters all this out, but there is nothing EVA can do to force Frontier to update their server state.

Updates in Elite:Dangerous 2.2 have made it potentially easier to get realtime updates, once EDProxy has been updated to match. When this happens, EVA will get updated to react to docking too.