Nifty Swiss Cover From 1917

It kind of reminds me of the trials of wartime, or who knows, maybe a pandemic...

At some later point the letter was handled by the military.Written below
'passé au 4° génie
Grenoble Isere'
Is there an address on the back ?

As a matter of fact, it does:

After being handled by the 4° Genie; I think the letter was then forwarded too the 30th Alpine Battalion(unknown 30°) -SHR (section hors rang)In red This was comprised of
A section of artificers, armourers, secretaries, ordinances, non-commissioned supply officers, drivers, blacksmiths and butchers.
They handled all the odds and ends behind the front.
There is a pencil notation in the middle reading 86eme A.. lourde:
which is the 86th Battalion of heavy artillery.
This letter went from one Battalion too another .The war was raging so there may of been some reason.
There is a cancel on the left but I can't make it out
At some point it was returned to the sender although there is no real proof of that.