A 50-move-rule claim turned out to be incorrect - can the arbiter punish me? I claimed a 50-move draw, but my claim turned out to be incorrect. Can the arbiter punish me by increasing the opponent's time or reducing mine?
Yes
According to the FIDE Laws of Chess

9.5.3 If the claim is found to be incorrect, the arbiter shall add two minutes to the opponent’s remaining thinking time. Then the game shall continue. If the claim was based on an intended move, this move must be made in accordance with Articles 3 and 4