I just spent too long on this so maybe I can save someone some trouble.
I had projectiles spawning on clients but not consistently: new projectiles would only appear locally most of the time, but every now and then they would spawn remotely as well.
After spending too long in my code I realized the pattern: The issue became better or worse depending on my turret rotation.
After further extending my projectile spawn point on the prefab, the issue disappeared. My guess is that my spawn point was within the positional margin of error caused by latency, and projectiles were sometimes spawning inside of the player and being destroyed immediately.
No problem here anymore but I thought it’s worth a share.