Stroke round cap being cut off when using "gradient along stroke"

Hi everyone!
I was trying to apply a gradient along my round-cap stroke,
but then the head of the stroke is always being cut or not showing properly like this:

I search through the tutorial apply gradient along the stroke and seems they didn't encounter the same problem.
Is there anything I set up worngly or any other ways I can do this?

Any possible reply will be appreciated. Thank you so much!