I haven’t made any recent set-up changes to my comments so had a look at Blogger Help, which recommended that I switch to a more basic comments set-up. This unfortunately means I can’t reply direct to comments but might hopefully solve the problem.
Also, apparently if you have ‘Disabled 3rd party cookies’ on your pc/device, this can also affect the comments too.
Oh and some say it could be an Apple issue, which Opera can resolve (I can’t really comment <ahem>, not being an iPhone or iPad user).
Apologies for any inconvenience.