Thanks for your suggestion, and for taking the time to describe what you've observed. We are aware of the issues we are having with the primary catalogue, and are in fact working hard behind the scenes to remedy them. The error message itself gives a somewhat misleading impression; we are not performing maintenance that goes on for days, nor is it really a capacity issue. The technical issue at the core of it is the interaction between two different servers, one which supplies the content, while the other delivers the McMaster-branded interface. We know there are issues, but they are proving elusive to nail down, but please rest assured that this is very high on our radar and we hope to eliminate them soon.
It's not a perfect workaround, but when this occurs, you can always use our Classic Catalogue (https://mcmaster.sirsidynix.net/ - also linked below the search box on our main page) to search the catalogue. It runs on a different platform, so does not suffer from this particular issue.
Answered by: Dale Askey (Associate University Librarian, Library Learning Technologies)