In Dorico 6, when a system starts with a repeat bar and a time signature, and the previous system ends in a double barline, the double barline collides with the cautionary time signature.
In Engraving Options > Barlines > Repeats > Barline at end of system coinciding with start repeat:, set it to Default barline (rather than Double barline), and click Apply;
then
In Write mode, select the repeat barline at the start of the second system, open Properties, enable Barline at end of system and set it to Double.
You might find that step 2 will produce the desired result without needing to do step 1.
Thanks, it seems step 2 does produce the desired result without changing engraving options; however, I would much prefer this to be automatic, as it was in Dorico 5.