Can you post a save/ruleset? City textures shouldn't affect landed UFOs...
I think I got what's causing the issue: if the location of a coastal city is set upon a land texture there isn't a problem but if the city is placed upon the ocean texture (the best example are islands) the game can't assign a terrain for the UFO landed there and the battlescape generation crashes.
This issue actually should predate the recent mission/texture changes, I just noticed it because I was trying to get the UFOs landed on cities during Infiltration to use city terrains rather than farm/forest/etc.
This issue might actually affect TFTD, if there are any cities whose location is on land (the opposite of the previous situation described) and a USO lands there for an Alien Infiltration mission, since the game won't be able to assign a sea texture/terrain for tactical combat.
I'm using the Terrain Pack to generate this issue, plus a missions test ruleset to ensure that the 1st mission generated is Alien Infiltration. I've attached below the Mission Test ruleset and a saved game where a UFO has landed on Nuuk (which is placed on land) and sending a Skyranger there will crash the game.
I can actually fix this on my own by editing the coastal cities locations so that they are all located on land. Or simply assign those cities to the ocean regions since there are no Alien Retaliation scheduled for those. I'm curious though if this issue has popped up in TFTD.