All these issues related with geoengine and movement systems. And never be fixed because L2J developers don't understand how it must work properly. This problem is due to the fact that need to have some basic mathematical knowledge and knows what client and server it's one whole and ignore some client/server data the big mistake.
No one don't tries perceive an object movement as a vector that has a direction, velocity and acceleration. All developers write a code imagine what an object moves by horisontal surface with constant speed. For this model he can't falling or slide with acceleration on inclined. About validation position it's really magic in L2J. Server side have absolute data and this is uses as true position. And "насрать" what client sends to server. LMAO
Only newbies tries to fing "better" geodata for resolving this issues but geodata related only with elegant final pathways for pathfinding's result (from point A to point B) and correct detecting objects behind an obtacles. That's all.
As @Trancesaid if you need actual geodata for your maps you can hire @deMEVfor this job. If you have some stuck places you can edit this places manually because any builder will produce conflict cells. If you have any other issues just use L2OFF platform. In next 5-8 years L2J don't resolve it.
Have a nice day.