I just started having this issue on 4.16 and it worked perfectly on 4.14. I know the reason, but not how to fix it. My 127x127 landscape on 4.14 made my landscape like 4k resolution while on 4.16 the same 127x127 landscape had a resolution of like 255x255. So however you raise the resolution of the terrain is how you fix this issue, if anyone knows, please post how.