constructive criticism (why have monthly/annual payment?).
Look, I understand that the costs of running a game like this may be high but I don't think this is the way to go about combating the issue or monetizing the game. To be honest with you these changes seem far too restrictive and to anyone who doesn't go to the effort of reading the reasons for this change it just seems like one giant money grab or scam. As an avid user of this application I found it a huge turn off and have recently just stopped playing, this is also the case for many of my friends and I feel the game may lose a large portion of its fan base. however if there is nothing else you can do, I would suggest not having a monthly subscription as the way of paying for the pro version, but instead have one outright cost that gives you the pro version forever, this would be a far more attractive option then the game slowly sucking money from your wallet.
Alternative to subscription would be "pay X to play Y times". This would allow players that don't play regularly to just pay what they actually play. But this also remove extra funding to the game which probably allows free players to play challenges for free...