I’ve seen this happen many times and it can be difficult trying to glue because of the wax potting solution on older pickups. Some reissue single coil P-Bass pickups are potted in solutions other than wax and I have carefully used a drop of Cyanoacrylate (superglue) carefully at the top of the pole piece using a glue pen. Hold the top down using a piece of wax paper as an insulator between your fingers and vulcanized fibre so you don’t end up walking around with a pickup stuck to your finger. Make sure you always wear safety glasses when soldering or using any chemicals especially superglue. Loctite Super Bonder 495 works well too. After lightly gluing the flatwork, carefully clean or scrape off any residue off the magnets using a non metallic scraper so you don’t scratch the surface of the magnets. If the job is difficult, have one of the qualified pickup winders carefully do the job for you.