I found the problem. It will be fixed in the next Maelstrom update. However, in the meantime, a simple workaround is to load different ammo, like cannonballs (which you don't have any, but that is no matter), then reload the hotshot ammo that you have. It will start the cannon loading process.
I did discover a flaw in the save-load process, where if you saved with specific conditions, it would not properly recognize the state of your cannon load and that is why it fails to render the cannon icons. I fixed that, but again, you can force the issue by reloading, but the scripts prevent you reloading ammo it thinks you already loaded, so just change type, then reload the ammo type you were having trouble.