I did migrate a big project from 4.13 to 4.18 and the biggest problem was that 4.18 wont package my levels because they exceeded 2gb memory per level (I am using static lightning). So if you get the same problem you need to divide your project in small levels (streaming levels) and build the light again (if you are using static lightning). The second thing I noticed is that I needed to remade all my glass materials and put new reflection captures. My project was of the arch-viz type, I am not sure how your game will work.
You can try to see if you will get some issues in 4.18 but I strongly suggest you to first find out why your map suddenly gets corrupted like that. I wouldn’t relax if I had a map that was corrupted in old version of the engine and suddenly the map works well i newer version of the engine.