Switch A and B are connected to each other with two links, we'll call those 1 & 2.
They're supposed to run STP or bonding or something to make 1 & 2 a logical single link, but that's misconfigured, misbehaving, or just plain old buggy.
By sheer bad luck, switch B has currently overflowed its MAC lookup table, and is falling back to broadcast for your destination MAC.
You send a packet to switch A. Switch A looks up the destination MAC, and forwards the packet to link 1. Switch B receives the packet, has no idea where that MAC is, and forwards it to links 2-n. Switch A receives the packet, looks up the destination MAC, and and forwards the packet to link 1. Rinse, repeat. Observe packets sent by switch B on ports 3-n.
They're supposed to run STP or bonding or something to make 1 & 2 a logical single link, but that's misconfigured, misbehaving, or just plain old buggy.
By sheer bad luck, switch B has currently overflowed its MAC lookup table, and is falling back to broadcast for your destination MAC.
You send a packet to switch A. Switch A looks up the destination MAC, and forwards the packet to link 1. Switch B receives the packet, has no idea where that MAC is, and forwards it to links 2-n. Switch A receives the packet, looks up the destination MAC, and and forwards the packet to link 1. Rinse, repeat. Observe packets sent by switch B on ports 3-n.