Wonderful new civ with very interesting mechanics.
Just some nitpicky stuff here, hope it helps.
The new settler unit is super cool. The coastal settling seems to work well. I love that it turns into a scout afterwards. One thing I noticed is, unlike with other naval units, if I am producing one and there happens to be an enemy unit occupying the only valid placement spot it doesn't cease production. From what I can tell, instead, it completed production but didn't spawn a unit. Another bug, the first point in the Expansionist tree (increased production for settlers) did not seem to apply to the new settler unit. Probably not possible, but if there were a way to let the unit collect coastal goody huts (on land) from the water that would be amazing.
I noticed there is a policy for "+2 Influence and +2 Happiness in settlements you don't own." Not sure if this is intended, but if so it definitely is an interesting concept. Unfortunately from what I can tell it doesn't currently work. It may make a bit more sense, if intended as written, if it does what it says but specifically, also, only for those Civ's/Leader's settlements that you also have an alliance with? Just a thought. If not, I fully support the insanity of cranking up everyone else's Influence regardless.
The unique improvement specifies "on a hill". I'm unsure what that means, and as such I was not able to find any suitable location for it. Does this mean on cliffs? If so, does it include coastal cliffs? I hope so if that is the case. Perhaps I got unlucky with the custom map I was playing.
In general the unique civics for the civ felt a little lackluster due to their narrowness, and definitely could use a bit of expansion with some added masteries in my opinion.
One idea I have for this Civ, as there are no naval commanders in Antiquity, would be to allow the effects of Army Commanders to apply to Lembus. It could even be a policy that lets this be the case for all naval units, perhaps, but I suppose that may be super OP in Exploration/Modern with other Civs.
I haven't played your other civs since before 1.10. I will give them another go and bring back some feedback for ya'.