Disappearing miles

I had 161,000 miles in my account but this week it's now changed to 155,000. I haven't used the miles so rang the flying club to query this as no transactions have been posted. They couldn't explain why as they also couldn't see any transactions. They asked if I'd taken a screenshot showing the 161,000 but I haven't as I didn't think there'd be a need to. They've passed the issue to a different department and said they'll get back to me. I've got no idea what could have happened?

A shopping miles transaction or two since returned, refunded and miles taken back? They backdate the transaction to the date that the miles were issued so it may not appear on the limited transaction activity view we seem to get at the moment - regardless of the criteria you input into the form, mine only goes back a month

No, not that I know of. I'll see what they say on Monday.