Comment # 1 on bug 991693 from Raymond Wooninck

The xembed-sni-proxy is not missing from Plasma 5.5.  The reason why the
package was removed and obsoleted is that it was integrated in
plasma5-workspace. 

So you should have the binary /usr/bin/xembedsniproxy on your system if you
have plasma5-workspace 5.5.5 installed.

Please check the following:

1) Does the binary /usr/bin/xembedsniproxy exist ? If not, please reinstall the
plasma5-workspace package and check again.

2) If it exists, please check if it is running. 

3) If it is not running, then please start it from a konsole and see if error
messages are generated.