I have two dwarven rings equiped (only blue rings I have), don’t know if that matters.
Happens almost every fight, though not all the time:
When matching red gems, some V-gems are created, but some of the newly created V-gems cannot be matched with any other gems. After another turn they can be matched.
Even if they appear in a spot where they should be part of a match immediately, they are not matched and can still be moved.
OK, after further experimenting, the V-gems have the wrong color. I managed to match them as another color than the color they are shown. Even when clicking them they indicate the color they have on screen, but they can be matched as another color, (not always the same color).
Can corroborate. Occasionally, the color of the gem will switch to the correct color, usually when a matching color gem skyfalls in an adjacent square.