Ah, nevermind - archers and bows are back where they belong. I still can't build Harbours no matter how close to the sea I am.

I do have the oddest things when not restarting my computer between games, though. Something's saved in the memory and doesn't get flushed with closing the game.

For example: One game, I went all the way to a tech-tree so that only Refines were left available. Starting another game, and the respective tech-tree (Civilization) remained empty for my new kingdom. Researching Civi returned nothing even though it increased levels. I restarted the game between these two matches. Restarting the computer fixed it for the next game started.

Same with the missing archers right now.