You don't mention the type of disks you're using with RDS.
Disk scaling/changing operations also consume IOPS to do their work which can get you into trouble if you, say, run out of burstable IOPS but RDS is still partway through a background mirror operation.
If you have RDS Enhanced Monitoring turned on do look at these metrics. They're a bit trickier to use but as they come from an agent on the instance rather than the hypervisor can sometimes help debug.
Like any company sometimes the support agent you get might be having an off day. This is where having an AWS TAM is helpful - you can get them to re-esculate the support issue for a second opinion.
If you have RDS Enhanced Monitoring turned on do look at these metrics. They're a bit trickier to use but as they come from an agent on the instance rather than the hypervisor can sometimes help debug.
Like any company sometimes the support agent you get might be having an off day. This is where having an AWS TAM is helpful - you can get them to re-esculate the support issue for a second opinion.