Weather is not based on the world seed

In older versions (from what I know, 1.12.2 was the last version where this was the case) weather used to be fully based on the seed of the world, i.e. rain/thunder would always start/end at the same time if the same world seed was used, but that is not the case anymore.

Steps to reproduce the issue:

1. open Minecraft 1.6.4;

2. create a new world with the seed -619559134183837125

3. wait 17 minutes and 24 seconds, after that time it will start raining and a bit later thundering;

4. create a new world with the same seed to check that that is always the case;

5. open Minecraft 26.2;

6. create a new world;

7. wait for rain/thunder to occur;

8. check the in-game time;

9. create another world with the same seed and wait again for rain/thunder, notice how it starts/ends at a different time.

Expected result: It always starts raining/thundering at the same time since that used to be the case, and also with every update more and more things are data driven / seed based, so there is no reason for that not to be the case for weather.

Actual result: Weather is fully random, even though it used to not be random (if the same seed was used).