Just as a general rule, precombs do not only mess with external texture swaps but also sometimes fences and stairs can loose collision. So always check this out and create a backup before doing this
yeah ive seen that many times... and sometimes simply regenerating the same cell again fixes the issue...
Now im going and sticking embedded objects (a small poster for example) into wall parts and making them scols so that they stay as intended...(stupid i know but its the easiest solution to my problem)