Hello Giovanni
The trombone effect is something that we see with first hop redundancy protocols such as HSRP and VRRP when you distribute layer 2 across multiple datacenters in remote locations. As in the example you shared, this effect results in suboptimal switching of traffic. The solution to this is the use of FHRP isolation which is applied in Cisco’s Overlay Transport Virtualisation (OTV) infrastructure.
FHRP isolation allows for the containment of the election process within each site so that a local device is always elected as the active device.
The following Cisco community post summarizes FHRP isolation and how it works to resolve this problem:
I hope this has been helpful!
Laz