After the first start, a default configuration is created.
File world_settings.toml, "Biome Temperatures" contain a predefined values, f.e.
["minecraft:jungle", 76, 87, "F"]

After the first entry into the ingame config (without any changes) temperatures in file will change to MC unit, but without unit change.
["minecraft:jungle", 1.0476190476190477, 1.3095238095238095, "F"]

And it makes it very cold in a hot biome. "F" should be changed to "MC".

Thanks for the report. This issue has been fixed in the patch I just released :)