Every of my dwellers that i sent to exploring, is finding max 1 item, never more. Even after 17 days of journey.

Did you mess with your system time? There was an old glitch that if you set your time way in advance you could trick the game into thinking you'd been out for several days so it gave more rare and even legendary items. That glitch was fixed, so now if you mess with your system date and time it will give you one item and nothing else. At least I think that is what happened.

Welp, I had some problems with date on my phone, but that was changing 1 day atleast.