Hello,

In cold biomes, ice become water. The biome is "Cold Taiga" and come from Biome Bundle that is supposed to not adding any new biomes but re-use vanilla ones.

There is no settings for cold biomes in settings, only for tropical ones and all ice in cold biomes are transformed into water that is cause a large water flow and lag in the server.

Thank you in advance!

I can't replicate this at all. Regardless though, biomes that were already snowy aren't really affected by seasons at all. You're likely in a biome that was never snowy to begin with and has a temperature above 0.15F

Ice should never become water in cold biomes.
Because at this moment, your mod is incompatible with Biome Bundle and OpenTerrainGenerator.

It doesn't. I just told you I couldn't replicate the issue, and that the biome you're in likely isn't snowy.

Even if the word "cold" is in the biome name, it is not snowy for you?
Is it a Biome Bundle issue then? I create a repport in their github just in case.

"Cold" in the name means nothing on its own. The biome temperature is what matters, and Biome Bundle/OTG doesn't add real biomes, instead using some hacky method of reusing vanilla biomes. We can't guarantee things will work when they're using biomes in a way that they're not meant to be used.

But the F3 says that the biome is "cold". You really cannot do anything about that?
A kind of "compatiblity" option to make that all biomes with "cold" in the name is not affected by seasons? I know that this is a really ugly method, but this could save the problem. I mean, without any reset of the map on our server. And with luck, water could re-become ice again.

My English is really bad, but I just ask you if you want to add this option. It's not an order, even if what I said let you thinking it. SereneSeasons is your mod and you have the last word on it, of course.

Maybe these infos can bring some insight hoping that I'm not inteprenting wrongly the documentation:
The Cold Taiga.bc , Cold Taiga M.bc and Cold Taiga Hills.bc configuration files from Biome Bundle states BiomeTemperature: 0.2 which according to the Minecraft standards:

The required values are less than 0.15 for snow, 0.15 - 0.95 for rain, or greater than 1.0 for neither.

I'm guessing that Serene Seasons follows the same basic MC mechanics for the weather so, if this is the case everything (Biome Bundle and Serene Seaons) is working properly and executing the code as expected.

with "cold" in the name

I'm afraid to inform you that Biomes characteristics aren't decided upon their formal name but by other settings which are often shared among the modders which use the basic MC standards as renference.