Black Sea countries can't trade overseas, so basically Ukraine, Romania, Bulgaria and any other country that have the Black Sea as the only sea, can't trade with US or Mexico and the like. But, US and other overseas countries CAN trade with the Black Sea countries. I use no other mods, the latest version of the game and the mod, all DLCs enabled.

The only temporary solution that I found is to have land bridge to literally any other sea or ocean, but it has to be connected to the mainland.