This morning I thought I should check the issue is not theme or plugin related despite not adding any new ones recently, so deactivated all plugins first and the problem appears to have stopped.
Now that I have a direction to head in, which appears to be causing the issue I should be able to narrow down and sort this problem fairly quickly. I am assuming it must be from a recent plugin update.
When I find the culprit I will post it here. It may help someone else.