Hi James,
It’s a long time since I did an edit to tape and I feel your pain, it brings back memories.
It could be that the deck doesn’t have an external reference signal and that’s causing the issues.
To fix this, and if you don’t have house reference into your deck, you need to loop the reference on the deck. There’s four BNC inputs on the top left of the deck. I think its take the Deck Ref Input (top left) and loop it with a BNC cable to the Deck Composite BNC input, the bottom right BNC of those four. I can’t remember if you need 75 ohms on or off. I seem to recall that on the Decklink breakout cable there’s a composite out so not SDI, that connects to the composite in, top right BNC, but that may not be necessary. It’s fifteen years ago when I last did this so I’m a bit foggy on the set up but it should work with looping the ref signal on the deck.
Your other option is to make your timeline longer, so add a few mins of black after the pic end, and do an assemble edit to tape. That moves the break after the sequence further down the tape.
Hope that helps,
Neal