Freezing client recovered only after re-sharing files

For apparently no reason my client started using up to 30% of CPU and became unusable, even if downloads and uploads seemed to be working properly. I tried re-scanning my shares (almost 120.000 files) and even reinstalling the app, but nothing changed. The only thing that worked was clearing and than re-sharing my files.

Why could this happen? And what can I do to prevent it?

sounds like a defective config file where this inventory is kept. A crash of SLSKqt or interupt (manually killing the client) while writing the config file could cause corruption. Saving (exporting) your settings from time to time helps to get fast started again.