Complete code and some example data would help. Copy the code from your editor, on the forum open a text box using the </> icon and paste the code.
Without knowing the current options you are using for the graph we will spend a lot of time guessing what you have and some suggestions may not work because they conflict with other choices made in your code.
I suspect that the value for that arrow is just too small. The length of the "cap" could imply a value not present in your data as it has a minimum size needed to display.
Edit:
I am guessing that you did a HIGHLOW plot. Depending on your settings for graphic area this may explain what happens:
data plot;
do y=1 to 25;
low=0;
if y< 5 then high=y/5;
else high=y;
output;
end;
run;
proc sgplot data=plot;
highlow y=y low=low high=high /
barwidth=1
highcap=filledarrow
type=bar
;
run;

Note that a "small" value for high, in this case 0.6 for Y=3, allows just the point but that smaller values of 0.4 and 0.2 there is not sufficient space for the entire triangle of the arrow so none is shown.