I am unable to reproduce this as well. Here is my sample f-key in my aliases.mrc file.
I used two slashes as prefixes because that's what you said you used, and it still works on my end. Though, the slashes are not needed and should not be used per style.
This replaces my F1 key to display "test" instead of opening the help file.
I do not know what "sddc" is in your f-key definition. It is possible that "sddc" is an invalid non-existent alias. Try deleting that word from your f-key alias definition and see if it works agian.
Also, you cannot use $$1 in f-key aliases. Delete that too and replace it with somebody's nickname, or anything else besides $$1.
($$1 will always behave as /halt in an f-key alias. Khaled and maroon aren't on their game today!)
//F5 sddc //gline $$1 3d :12Floodbot / Drone / Abusive (set by Chris at $fulldate $+ ) (fab)
F5 gline Khaled 3d :12Floodbot / Drone / Abusive (set by Chris at $fulldate $+ ) (fab)