When you cut dynamic trees in snowy biomes, snow stays in the air, unlike not dynamic trees.

https://imgur.com/a/kIKnSNI

Oh crap. That's nasty. I wonder how I never noticed that.

Was this in single player mode or was this on a server?

It's multiplayer. For testing purpose, I play on a client connected to a server on the same LAN.

I'm unable to reproduce this no matter what I try. Singleplayer/Multiplayer Creative/Survival or what have you. Could it be possible there's some kind of other mod interaction? Could you do a test with just dynamic trees mod installed?

Maybe it's Serene Seasons, from which the snow come from.

Can you temporarily remove Serene Seasons and make a new world and test it?

Even without Serene Season, issue still remains. Here in Ice Plains or Cold Taiga :

https://imgur.com/a/r7d2thn

I have 170+ mods, it would be difficult to find the one in conflicting.

The issue occurs only in multiplayer mode.

After the snow is hanging in air can you log out and log back in to see if they disappear?

The snow stays in the air after logging out and back. Same thing after a server restart. I have to break the blocks manually.

Here's what we know:

• It's a multiplayer only issue.
• I'm unable to reproduce the problem even with multiplayer
• It's likely an interaction with one of the 170 mods.
• The error is not a client problem since logging out and in doesn't make the blocks disappear
• The issue does not appear to be tool related and happens every time however a tree is broken

Typical method for determining which mod is causing the problem(divide and conquer):

1. Remove half of the mods.
2. Test
3. If the problem persists remove half of the remaining(or recently re-added) mods. Go to step 2.
4. If the problem disappears then the problem is in one of the removed mods.
5. Re-add half of the previously removed mods. Go to step 2.

Using this method one can determine the bad relationship with a max of 7-8 iterations instead of 170(one at a time). In this case it's a problem because the mods need to be removed from the server and client as well and that takes more work. This is because it's a multiplayer only problem.

The best I can do at this point is to ask you to list the mods you are using. Maybe something will stick out.

Here's the list :
http://modlister.com/server/IndustrialScience

I may take some time to find out the problematic mod.

Unable to reproduce / Issue is not productive

I should have thought earlier, it's FastLeafDecay. I forgot i used this one. I open an issue on his github pointing to this one.