We have 20 consumers distributed across 4 regions. The multi master providers are in region A, and we have 8 consumers in region A, 4 consumers in region B, 4 consumers in region C, and 4 consumers in region D.
The consumers located in the same region as providers, region A, cross availability zones but we do not have a proxy between consumers and providers, they dial directly to providers. The consumers located in regions B, C, and D have to go through a transit gateway but there is no proxy applications otherwise. Oddly enough we see the most issues with the consumers in region A, so I do not believe the transit gateways are at fault.