I play Civ 5 regularly with a friend. So we are using Steam / multiplayer / Internet.
The problem comes after we save and then load the game later.
The first player has their turn, then the game effectively ‘freezes’, because the game says it is ‘waiting for (second) player’ - but they cannot move anything.
Apparently this is a known fault - but has anyone got a solution?
Thanks for your time. 
I do not know if this works but I found this…probably worth a try at least:
It’s a common problem during multiplayer civ that when reloading, at least one person (Usually the host) will be unable to move. The way this is fixed is by having one person (anyone other than the host) leave the game as soon as it is loaded and then rejoin the game while it is in progress. Note: They must join as normal and wait until it is loaded before they leave and rejoin. Also if multiple people try doing this at the same time it can cause issues, so its best to agree before the game is reloaded who will hotjoin and let them do it. - SOURCE
Thanks for that - we’ll give ut a try!