I have the same problem that is described here.
The user cnzhx has posted a possible solution for OpenSUSE users.
My permissions of fusermount are
$ ls -l fusermount
-rwsr-xr-x 1 root root 31360 13. Dez 2016 fusermount
A trusted group doesn’t exist but I’m not sure if it should exist on Antergos/Arch in the first place. Is there anyone who has deeper knowledge about Arch who can help me fix this annoying KDE Connect bug?