Not sure but looks like deduped history doesn't work as expected when using custom normalizations. My undestanding is that the deduplications gets overwritten by my custom dbt? source - MongoDB, destination - BQ

Are you using only custom transformations or did you keep the Basic Normalization on?

raw data + custom transformation

Did you export the dbt module built by Airbyte and changed it? Because the Basic Normalization using incremental + dedup do the work you need

nope. Created my own from scratch. Where can I find it?

does it require access to the server itself to explort the normalization models used? We have our instance installed on our own server but I have no access to the backend.

Yes, you need to have access to the backend.

BTW, is there an option to use dbt models from a private github repository? I am afraid a public repository can expose sensitive data

Yes there is a guide in our docs