I went on a trip on my boat to another island and I realized that the map was updating. What I see is that the oceans are now just one single blue colour. Before (as you can see by the rest of the map), the oceans have different colours and you can tell which part of an ocean is a warm ocean and which parts are not.
Based on this:
https://www.minecraft.net/en-us/article/village---pillage-out-today-bedrock
and also my personal observations, it seems like this issue has been resolved.