+xTim, you have SkyDemon 3.10.4. You need to update your SkyDemon to 3.10.5.
Tim (and Dan), thank you both for your prompt replies. Seems I made a newbie error in that I have been regularly accepting the chart updates but didnt realise that I had to go back to the App Store to manually load the SD updates. So, in fact, I was running 3.10.0.124. No wonder perhaps that I was experiencing problems once I'd loaded iOS12. For interest Dan I'm using an iPad Mini 2 Cellular 128MB.
Weather permitting I'll be flying again next Wednesday and I'll gladly give feedback on any DI lag issues if I experience them.
Cheers again,
Tim