I have been having the same problem. Tried it on 2 different computers, using Firefox and MS Edge and contacted The Pocketmags help desk and received this answer:-
Thank you for your email!
We have recently been contacted by a large amount of publishers regarding a change in their piracy policies which we are trying to resolve. So some titles currently have printing suspended but we are working to get this feature back up and running as soon as possible.
We apologize for the inconvenience but with the upcoming changes we are looking to make page printing more user friendly and to allow for the PDF printing for a lot of titles.
Please note this is not permanent and will be available very soon.
Warm Regards,
Pocketmags Customer Service