Thanks for your comments.

Yeah, development is a problem if you don't have enough resources, but your main problem here is the different faith - I'm guessing an uncommon religion (or a Christian faith non-Catholic, non-Orthodox) for Central Europe.

Foodstuff should be more than enough in Central Europe, but only for those who have the same religion as the holder of exporting baronies, which are centered in Bohemia, around the Rhine, and Northern France iirc.

This happens because the mod takes Religions (also dividing Catholic vs. Orthodox vs. Other Christian faiths) in combination with Trade Regions, as you can see here: https://ck3mod.com/trade-routes/

Manually adding all that means that I have more control over historical accuracy of trade flows, but it's also really bad for 'more adventurous' campaigns. Say, a Viking conquering Cordoba or India would not fare well with this mod, however fun it might be with Vanilla (that is, if they don't have tribal government, because tribals don't use resources).

This approach has some advantages, like heresies becoming an easy prey for surrounding religions (as they always were). So, you won't easily see Adamites spreading throughout Europe, but rather them being sacked and enslaved... but it has a big disadvantage, which is what you are experiencing.

You can try two things:

1) Set the game rule to increase the relevance of local production over exports. Local production will never be enough, but this rule might help you (and will certainly mess with other realms, so the field is levelled).
2) Try to conquer exporting baronies as soon as possible. Once your religion gets hold of a productive barony, it will improve exports into any titles held by an independent ruler of your religion. You can see exporting baronies with the mod Trade Maps DTR.

At this moment I'm not planning to change the way trade flows work. But, I still have as a project the suggestion of another user: to be able to turn a barony into a productive (i.e. exporting) site. That could help solve things with gold instead of conquests.

Well, in a sense, I'm not that much bothered by those penalties themselves like by the thoughts that my citizens are starving and dying over the rampant disease. To be able to solve this with the money would be great, because that's my wealthiest resource.

Since I don't want a larger realm, I'm currently spreding my faith with underhanded methods, however, I still see no difference. But it doesn't matter. If it's not bug, then I'll find some other way to optimise this.

Thanks.