I mean these things did happen, just not at the front when you are fighting each other directly, but for example in POW camps they did happen.
Like for example, this is a story from POWs in a camp in Omsk in 1917:

"A lot of us prisoners of war in Omsk understood that we had to support the Russian workers in their struggle.
Even here in the distant Siberia it wasn't just about the revolution in Russia, but about the fight to free all the workers of the world.
We didn't just want to stand on the sidelines and watch, but form our own battalion, maybe even 500 fighters strong.
That is why we called a meeting in the camp of Omsk, in which comrade Thomann explained the situation to our fellow comrades.
He was excellent in getting the point across how we, even in our position in Siberia, could be of aid in supporting Soviet efforts in the European part of Russia.
If we could hold the Whites here in Siberia and in the far east in general, then they were unable to bring their full power down on the central parts of Russia.
By standing our ground here we could, even if only a little, aid our comrades in their fight.
We passed lists around so everybody willing to fight could sign, shortly thereafter 800 people willing to fight had signed on."

• Ferdinand Effenberger, Source: Illustrierte Geschichte der deutschen Novemberrevolution 1918/1919 - p.24

Here is a picture of former German, Austrian, Serbian and Hungarian prisoners of war, now Red Guards.