The carbon speargun included in the starting crate only works with the 4 carbon arrows provided. Using standard speargun ammo afterwards is impossible, rendering the carbon speargun effectively useless.
Seed: 18305136
I started this save with default settings (aside from enabling the starting crate). It is a multiplayer save. I have used custom islands on this save. I also change the wildlife settings between default and passive from time to time.
Steps to recreate are quite simple: Start a save with starting crate enabled. Use up carbon speargun ammo. Craft more speargun ammo. Find that you cannot load your standard speargun ammo into the carbon speargun.
Reloading the game, restarting console, clearing cache etc. does not help. The only workaround I’ve found is to simply not use the carbon speargun at all.
Note: The craftable speargun works for the craftable ammo. It does not appear to work with the carbon speargun ammo. I would speculate that both tools may be missing flags to make them compatible with the other’s ammunition despite them being of the same type.
Love the game, and I regret that my first post here is a bug report, but since I didn’t see it listed in the known issues category (and because I would really rather use the carbon speargun than the normal one 
) I thought I ought to make it known.
Thanks for your time and cheers for all the hard work ironing out bugs.
