Hi Marc, apologies for the belated response,
I've got a timeline for the events as follows;
User renewed an existing subscription on May 1st,
User Cancelled renewals of the subscription on May 25th
User upgraded from subscription to higher subscription on July 4th
User paid the upgrade amount on the same day.
User's subscription expired the following month "Expiring purchase (UPGRADED TIER) changed from (UPGRADED TIER) to Multimart (LOWER TIER)".
From what I can tell, the user's upgraded subscription, expired then down-tiered to the previous tier, instead of being placed back into the group they were originally in at the start... Another anomaly here, is the grace period was previously set as three days but was changed down to one; That doesn't seem to have affected this specific subscription, unlike the others it did affect.
Due to the nature of this, I can't reveal a lot publicly; If more information is needed feel free to let me known some options in terms of private communication where possible.