[GS] Trading away cities...

[Tech Osen]

Somewhere in the distant past the filthy Aztecs conquered a couple of cities from the glorious Scots. Some time later I became allied with the Scots but that didn't discourage the damnable Aztecs from starting a new war. A bad call on their part. I quickly mobilized and decided to right the wrongs from the past and conquered
Scone, Haddington en Aberdeen (in that order). I didn't liberate them right away because I wanted to avoid loyalty issues and was planning to give them back after I got those three cities and Edinburgh back. I conquered Edinburgh, liberated it right away and then made peace with the Aztecs.

Now the reason why I posted this: at first I could only trade Scone back to the Scots. Haddington and Aberdeen were simply not in the list. At first I thought it might have been a loyalty issues but while Aberdeen was still recovering Haddington was already at full loyalty. A couple of turns later Aberdeen, still not at full loyalty and conquered after Haddington, was in the list and I gave it back. Haddington however is still not available, I didn't keep count but it must have been a dozen turns at least.
So my question: does anyone know the rules behind all this?

Edit: couple turns after this Haddington did become available. Could it be a size thing?

 

[Victoria]

I had a look at it and it matched loyalty 100% but did not test many times. Surprised it is different, is the save unmodded?
It may be the same issue a rew other things have that the EOT is not updating everything every turn. Once 100% loyal, save and reload, and then check if it’s tradeable.

 

[Tech Osen]

Only three mods:

Better Report Screen
No Appeal Penalty from Wilderness
Environment Skin (civ V terrain).

Like I said: Haddington became available for trade a few turns after the screenshot.