Hi Fiona
It's a frustrating issue, and one that we don't have the resource to explore in too much detail, though we tried all the obvious settings (see reply to Craig below). We've just stuck with the solution that works because our LMS has been tremendously busy over the past 2 years.
On a side note, we've found that our completion recording and general functionality issues have escalated during the pandemic, when all our users were at home on a variety of devices/browsers.
Good luck with it, and if you find a durable solution, please post it here.
Best
Jane