Sounds like the machine was a mess. It could be somthing mechanical, but it is doubtful. Is the machine plumbed in or are you running it from a bottle? With a blind basket in the portafilter, your brew pressure gauge should be around 9 bar. Grouphead pressure will be slightly less. If it is plumbed in, what is your input pressure? Max input on a sixties is 2-4 bar.
Coffee, regardless of where you got it, the first question is when was it roasted? You should have a roasted on date on the bag. If not toss it and get some coffee that does. The roasted date should be no more than 10-12 days ago, 3 or 4 days would be best. That is not a 'scooped on' or bag opened date but when the coffee came out of the roasting drum.
Mazzer, the adjustment stop screw is probably still in the adjustment color. Take it out, it is a small phillips head screw. The ground coffee should have a consistency close to table salt or a little finer to get started.
Dose, elektra does not like a high dose. Do you have scale good for 0.1 gram's? You should get one to make sure you are dosing consistently to start with. Elektra likes around 14-15 grams of coffee in the stock double basket. You sould not see an imprint of the shower screen or shower screen screw on the puck after the shot. Dosing should be slightly below the rim of the basket before you tamp.
Flushing, the elektra needs no recovery after the cooling flush. 1.2 bar on the boiler pressure is a bit high. You should turn it down to around 1 or 1.1. Flush until the flash boil finishes, then go another 5 seconds. Stop, lock in your portafilter and pull your shot.
You may want to look at
Dialing in a new espresso machine, a step by step guide as well.