This mornign (5/16) I was suddenly disconnected with the message that "you have been disconnected for maintenance on your character"
There was no warning and it occured during a boss fight (which I had to repeat).
Since that disconnection I have been experiencing a problem that if I discard one card from my hand, one or two other cards also often disappear. This is making some fights unwinable as health cards or attack cards that I needed disappear along with the one card I intended to discard. I've had to resort to not discarding at all which is making things more difficult. I just fled a boss fight because after discarding one card, half my hand disappeared including two key attack cards and the health card I was about to use!!!
Still having the problem, but I've noticed what appears to be a pattern to it. The cards that disappear are usually adjacent in my hand. It seems that when I right click to discard, if i do not release IMMEDIATELY, it will discard the next card, sometimes the next two cards. A way to fix this would be to ensure that discards must be individually clicked to discard.
I don't know if this will help you, but, I've noticed when my internet is slow that I need to wait a moment or two before discarding anymore cards.
Between my unstable connection and the fact that cards will get slightly rearranged when you discard and/or enchant a card with a sun boost, I've found myself discarding or using the wrong cards often.