@ubi-thrupney

no peace on this subject. Just conquered another island in the new world (named it Cordoba), this time in the southern corner of the map. After settling on it I set up a new tradingroute only to discover a little later, that here the ship was hanging at the border of the map. It did load at a first port on an island nearby but could not make it to Cordoba. Info: I did switch back to DirectX 11 as the game as a whole works smoother this way. In one thing I was successful: I managed to find the screenprints.. Here they are:

To continue this saga:

The dream about my island "Cordoba" truly functioning is only partly sweet. Unfortunately it still has some aspects of a nightmare.

Placing the oil-port and a loadingdock at the west-beach quicksmart upset all trading routes again. Moving the oil-port to the eastcoast and deleting the loadingdock solved the problem. But I must send all ship the long way around the island.

Just after this I noticed a Great Eastern on the Cape - Map following a strange path along the edge of the map. Not expecting I boat there I made some inquiries: the ship was returning empty from the Old World to the New. Had no business whatsoever to be at Trelaweny. Whilst the greyisch lines led me to believe the ship would go all along the south-western edge of the map all of a sudden the captain decided to turn and head towards his proper target. - Yes, logbook and screenshots can be provieded upon request.

Dear friends at ubisoft: get rid of all the rum and beer on the captains decks and perhaps on some other places too and fix those GPS! The sooner the better. Just imagine one of the ship falling of the plate and breaking. The captians wellfare-league (of which I am a non-paying member) will be after you.

@ubi-thrupney

so your also on the issues on ship popping up in places they have no reason to be? And the problem, with setting routes that - whilst on the route map - it isn't possible anymore to move the points of entry to a world?

But great, I am looking forward to the solution of the main concern here. Thanks in advance!

This is a realy veird bug for it hardly follows an easy to determine pattern.
Reading up on different treads to the theme the one and only clear thing is this: The only common ground is "conquered island is not accessible". But to the where (which map concerned) and the how, the when (under what circumstances) and possible fixes player's experiences different vastly. So good luck to ubisoft to find and kill this beast.