The information you filled out should now be listed below. 
Basic Info:
Platform: Steam
Issue Type: Gameplay
Game Mode: Online Official
Server Type: PvP
Map: Exiled Lands
Server Name: 1395
Mods: None
Bug Description:
Every time I use the potion of natural learning, I lost the knowledge of Serpent-man Javelin.
Bug Reproduction:
Just use the potion of natural learning
This has been a thing for a very long time. Possibly since game was released. Knowledge stuff that you find in open world and/or dungeons are not part of your character base knowledge spreadsheet so to say, therefor whenever you consume a potion to wipe all your knowledge, those knowledge skills are also removed and you have to run back and learn them again. Why you wonder? Because… Yes.