Hi Walter,
Workaround :
You go through the comparison of TL. You can use syncs playheads at the same time (3 dots right).
TL1 is played on the left screen, the TL2 is played on the right screen.
By clicking on TL1 or TL2 we have the TL which has the focus on Decklink.
We edit TAB, with GANG ON, we can not use the playhead of the source.
compare.jpg