Jokes aside (but kudos to him, since he allowed me to use these screenshots), Frida’s mana started flashing from the moment I first matched three blue tiles.
Nothing weird was going on apparently.
After maxing her mana and using her special, everything went back to normal and mana bar stopped flashing.
I saw some closed topics from a few months ago with this same problem, but the problem seems to be back, so thought it was better to report it here.
PS. I have the combat recorded if it was needed.