It's such a shame that both CoMaps and even OsmAnd have massive issues with public transport routing - I don't blame them as it's a really complex problem - I just wish I had alternatives to gmaps ;(
I'd bet it's a data issue, not related to the apps themselves. I use a lot of public transport and contribute to OSM as much as I can, but contributing routes really recquires a special kind of commitment, one that likely needs to be paid for, so you can sit the whole routes with your GPS from begin to end. Specially in big cities where routes can take more than an hour, and there are so many.
I think processing GTFS data offline and on-device might be really challenging. There's OpenTripPlanner, which is web-based and can be self-hosted on a VPS (an example).
Do you not have an app run by the public transport company? That's what I use, and it's guaranteed to be up to date
It still crashes when I try to get a walking direction... it does not happen with driving or bicycling directions, just walking.
CoMaps
Cooperative community open-source fork of Organic Maps, an offline privacy-respecting not-for-profit OpenStreetMap GPS app for your phone.

