I've been having similar problems on the pokerstars UK build 49.0.0.553 - ive had invisible holecards and not being able to act, also the HUD only working on 1 table.
I emailed support and they claimed its packetloss on my side, spoke to ISP they say there's no problems. Never had a problem till about 4 days ago, are you experiencing similar?
Sometimes I also can't act mid hand and time out - been a source of major frustration