MAX485 suddenly drawing too much current and output voltage levels are not right
They use a MAX485CSA to communicate but suddenly one of them is drawing too much current


That sound like latch-up. It's what you get when a pin goes outside it's supply rails.


  Things that solved the garbage problem under any circumstance: joining the circuit's common ground with the power supply's ground (Earth), joining both sender and receiver GNDs, adding pull-up and pull-down resistors to channels A,B at the receiver's end.


You should already be doing this.
RS-485 is differential signal, but it still requires signal ground to keep the common mode voltage within spec.

I think this is going wrong here.