black floor and invisible walls

Are you running any mods? Mod bugs tend to be the main source of this issue.

no mods at all. it only happens when caves are enabled .

With DST closed, try running the "verify the integrity of game files" via Steam. 

Still having the same issue even uninstalled and reinstalled.

Edited January 9, 2020 by Sosi

can you enter the world that is having this issue, wait around 10 seconds, close DST, then attach the following log files?
\Documents\Klei\DoNotStarveTogether\client_log.txt
\Documents\Klei\DoNotStarveTogether\<your steam id>\Cluster_1\Master\server_log.txt
\Documents\Klei\DoNotStarveTogether\<your steam id>\Cluster_1\Caves\server_log.txt

Where <your steam id> is your seam id
and replace the 1 in Cluster_1 with the number of your save slot

server_log.txt

server_log.txt2.txt

client_log_2020-01-09-13-39-17.txt