In old buildings where the electrical wiring is dated, plugging in a high drawing current machine like a vacuum
will cause stress on the circuitry and cause lights to flicker.
The problem may with fluorescent lighting may worsen when the bulbs
themselves are on their last legs.
If you mention to the owners of the building or the tenants occupying the office
that the bulbs need to be replaced they may look after it for you or you can simply change them yourself,
the bulbs are relatively cheep. If you change the bulbs and they still flicker, there is most likely a weakness
in the electrical circuit involving the lights themselves Fluorescent lights have transformers built into them
that can also go out ( there's usually a strong humming noise to them when they do )