Those horizontal lines are a long-standing problem in FT that often seems to be related to rivers crossing the -180/+180 longitude line. I've been unable to track it down despite many hours of effort (and special code in the software intended to eliminate the problem). I vaguely recall that shifting your projection slightly may help.

One possible solution is to save your image in to halves, but that's not an ideal solution by any stretch of the imagination.

There isn't a 64-bit version of FT planned at this time.