If they are equally spaced around the building then they are fitted as a form of damp proofing. The plastic covers normally cover the ends of a porous tube which, in theory, allows dampness in the wall to evaporate away. I have never used them and, from what I hear, are only marginally effective. They do get blocked up with salts over time, which can be cleaned out, and it looks like they have been partially painted over which won’t help.

I would suggest having a very careful look for any dampness in the property and get a good surveyor to have a look at it.