Hello ,
I have an issue with the use of Grav on our website. The issue is that Google does not index 31 pages. If you could tell me who I could contact for assistance, I would be extremely grateful.
Google 
I don’t think that Grav is the issue here…
It can be plenty of reasons why page wasn’t be indexed… You even didn’t mention when pages was created…? are they in sitemap…? did you pass sitemap url to GSC? how you use canonical tags on your website…?