Fresh install of F26.
First user created in the installation process, no issue.
2nd user created with kuser from 1st user session.
This second user cannot log in from sddm but he can log in from a
terminal and run startx which works fine.
Apparently, everytime he tries to login from sddm, we get this in dmesg:
[ 8867.558759] sddm-helper: segfault at 0 ip 00007f141e369b1e sp
00007ffca5cf19f0 error 4 in libc-2.25.so[7f141e2f7000+1c7000]