I’ve experienced this anomaly ‘occasionally’ (not all the time) through various recent Avast versions however I have ignored the glitch and simply ran the Scan a second time.
I’ve seen this issue mentioned in other topics over the months and believe Avast is aware.
Thank you schmidthouse and DavidR for that information. It happens on more than one Windows PC and with both Windows 7 and Windows 10. I shall follow your advice and make second attempts to run scans.
It feels better to know that it is not my fault thanks to others confirming the problem’s existence.