Both on android phone and on PC emulator.
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.