Ok, it’s been a while since I tried to upgrade. 0.18.1 has been doing just fine for me. I’m trying to teach my son how to write blog posts using Hugo and of course “brew install hugo” for him gives him 0.25.1. But when he runs ‘hugo server’ some of the links generated in the archive don’t work.
As to getting 0.18.1, you can download it at the release page (not sure how brew works in this department)
As to what the reason behind your problem: That is impossible to guess with, like, no information. Any error message in the log would help. A link to the projcect source would be good.
Read the Release Notes for every release and pay particular attention to the Notes section. We usually call out breaking changes and deprecated features in the Notes section.
If you’re several versions behind, consider updating to the latest minor releases between 0.18 and 0.25. So, build with 0.19, then 0.20.7, and so on. We will sometimes log warnings for a couple minor releases on deprecated features before we remove those features (and the warnings). You may find clues along the way that will help you upgrade your site.