The elevated lines between buildings are rarely protected from a build up of a static charge as routers and bridges were not built with this in mind. On the physical layer, both ends of the wire are terminated into an isolation transformer with no discharge path to ground. This is an installation design fault against the guy that designed the installation. Lightning protection is often a gas discharge tube for a lower breakdown voltage. A high current discharge through a protection device can produce a relatively high ESD pulse through the transformer into the tranciever chip resulting in corrupt data to failures. A link between buildings must include a bleed discharge path to prevent the build up of voltage on the wire, or a shielded wire with grounded shield should be used.
Engineers design systems. A good technician can make them work.