Easy to explain, and very easy to solve at all. Best example, at the east of the hospital in Kavala are different rocks. One above the other and inside of others, very often it happens that player glichts into the stones while moving at the top. (or crouching around) The corners are very sensitive.

How to solve: Place invisble flat models above the rocks. The player is running on the flat models instead of the buggy stones (it can happen that it looks like the character does not stand exactly at the rock, but it prevents glichting inside of the rocks) {F23785} {F23786}