Thank you Ernst for your help,i try to give all the info what i could,BUT am not computer genius age is a factor
(64)but i try to answer to all point.
1.Raspbian GNU/Linux 9 (stretch)
2 try to connect WIFI
3 My comp is connected wired (cat5)
6 DHCP assigned IP-addresses
7 Raspberry by it self
9 sorry i do not know what is gadget mode
10 did not try because first pi is 3B+ and i run from usb stick.second pi is only 3B not+
11yes i reboted the router but all hell got loose,first RPI stop working for seconds and then restarted but with different IP address but i could fix that.
12 try to use on-board wifi
13 yes on my router 192.168.1.2 and ip scanner 192.168.1.2 and ifconfig on raspberry is 192.168.1.2
14 not wired
15 If on WiFi: is client separation disabled? sorry i have no clue what is that.(my wife knows what is that)