Your user is in the dialout and tty groups so it should not matter which. You may have a udev rule which is messing around with permissions and group ownership.
The problem I see here is group read access has been removed.
crw--w---- 1 root tty 166, 0 Μάι 10 16:06 /dev/ttyACM0
This is how the Arduino appears on my system.
crw-rw---- 1 root dialout 166, 0 xxxxxxxxxxxx /dev/ttyACM0
The following article covers "cannot open port" problems and how to fix them.