Now that few months have passed, I’m a bit surprised that I haven’t received any rent increase yet after the reference interest rate increased in June and I wanted to understand how common it is. What about you? did your rent increase or is it planned to increase?
It depends on where the reference interest rate stood at the time you moved in.
If you moved into your current apartment before March 2020, they were not allowed to increase your rent based on the reference interest rate, unless you asked for a rent decrease when the reference went down in the past.
Good point, I moved in after March 2020, so they can ask for an increase. They just haven’t done it yet.
I am on a fix them contract for 5 Years so I am not concerned before 2025.
In Geneva they are called ldtr.
Being a landlord on the other side of the table, we never increase rent during a lease. We only adjust (if needed) when tenants change.
Well until recently you would only be adjusting downwards - so reasonable not to, since it would not be beneficial for you as a landlord. 
This is wrong, if you asked for a decrease when the rates went down they are for sure allowed to increase. The rate on the contract is only valid if it was not changed in between.
That is true, my bad.
Since I don’t know anyone who asked for a decrease, I falsly assumed, that this would be the case here also.