What does the bill details screen show? I manage an AWS bill and I find it overly detailed. Others mentioned leftover EIPs, but the bill shows these as their own line item.
Not saying it can't happen, but I've never seen an 'Other' listed on the bill details screen. As I said above, it's detailed to a fault.
Actually it looks like this is for an EBS snapshot. Now it seems like EBS is a Lightsail feature, and the Lightsail console says that I don't have any storage or snapshots? Hm
EBS is also the general external storage attached to an instance. Go the ec2 console and look at snapshots and you should see it there. They are region specific, so make sure to select the region referred to on the bill.
I haven't used Lightsail, so I'm not sure if those snapshots end up in the general ec2 console. But, if you already checked the LS console and didn't see anything, then they must be in the ec2 console.
Not saying it can't happen, but I've never seen an 'Other' listed on the bill details screen. As I said above, it's detailed to a fault.