I don’t recall a problem with vertical lines, just the interlace detection. I’m using the Commodore 390682-03 adapter, which re-generates H+V sync from the composite sync signal as opposed to directly using the H and V sync signals (pins 11 and 12) from the DB-23 port. This specific adapter is needed with the Video Toaster since the H and V sync lines become useless when genlock mode is activated on the Amiga.
The normal 390682-01 is a simple buffered sync adapter. It uses a 74HCT08 to double invert the lines.