I suspect that even though the character is coded, the function will interpret the coded character as it normally does and still truncate the result (because it's being passed to the function).
Maybe use the function 2x and a character code, so that the left and right parts are individually passed to the function but the character isn't involved. Like
BULLETIN: HyperlinkPart("http://172.12.317.33/service/ycyc.php?/",1) & Chr(35) & HyperlinkPart("/name=" & [TABLE1]![COLUMN6],1)
I note that your example uses semi colon ![COLUMN6];1
but I don't think that is the main problem.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.