Also, when it happens... And before you stop the server...

Run these commands in your Linux console:

ulimit -u

ps -elfT | grep -i arma3server | wc -l

Edit!
Run them with the same user you're running the arma3server with.
And paste the output here.

I will add extra information on the threading error and send you a new file so we can conclude what's happening.

Download the latest aliveplugin.dll from war room and see if it gets better.
http://alivemod.com/downloads/@aliveserver.zip

Edit:
Send me the plugin log anyway. It'll be helpful to see what it was doing prior to the crash.

You were on Linux, right ?
I'll PM you a with a new file you can try out.

@aliveServer or @aliveserver ?
You should lowercase the foldername.

Your ldd output is good, so the plugin should be working now.

Edit!
Your plugin might be corrupt as well.. You should download the new plugin from the war room.
The plugin should be around 1.9MB.

Edit #2!
I just saw Friznit posted something about that earlier here. So disregard my first edit =D

Sorry. Seems like libcurl.so.4 is actually from libcurl3 and not libcurl4.
Try:

sudo apt-get install libcurl3:i386

Then this should work:

sudo apt-get install libcurl4-openssl-dev

Try this:

sudo apt-get install curl

And then check the 'ldd' output again.

If you haven't used your War Room group before, I'd suggest you delete that group and create a new one.
Make sure you use a unique group tag. Don't use "Arma 3". It's not unique enough.
For example, I would suggest "BFS" as your group tag or something like that.

What's your group name ? Is it "Arma 3" ? If not, you should re-download alive.cfg.
If you go to War Room and click "Your Group", then the groupname in alive.cfg should be whatever is between [ and ].