AirPrint no longer compatible with canon printer?

Hi, a pensioner couple I help out on the technology front have been using an iPad 2 and iPhone 5 and printing to a Canon MG5460 via AirPrint for about a year without a problem. Then one of the Apple software updates to their devices about a month or so ago broke AirPrint somehow (don't know which update). The devices are now talking enough to trigger printing and paper load, but the printed text etc isn't transferring - i.e. pages are coming out blank.

I did a firmware update on the Canon device thinking that might solve it. But it has made no difference, the problem still exists. If I print via iPad or iPhone there is no text printed. If I print from a mac via AirPrint some text is printed but it is clearly distorted and fragmented.

They do all their document printing through Pages but since the problem started I downloaded google docs and also tried via that - same result. Everything seems to be in working order on the hardware front except the AirPrint data transfer part.

Does anyone have a suggestion on what to try next?

Thanks