Strange printing problem since iOS 11.2.5

Has anyone else had a problem of some characters being 'smudged', I use this term very loosely, when printing form their iPad with iOS 11.2.5 to an AirPrint enabled HP printer.

I use an HP OfficeJet 8620 which prints fine using AirPrint form my MacBook Pro but messes up certain characters when printing form my iPad. The letters most affected are 'M', 'W', 'Y' and '\' other letters all look fine. In the case of the 'M's I get a big black triangle printed above every 'M' for the 'W' and 'Y's it is almost as if they are part printed in bold. Printing the exact same document form the MacBook Pro over AirPrint gives no problems and the text all looks very clean.

Just trying to ascertain if this is an iOS 11 thing or something to do with my kit.

Thanks in advance for any feedback.