A while ago i played this game already till the end (0.4.2c), now i downloaded the version 0.5.25 and started a new game. After a while i entered Gorn and went to the marketplace (because one of my girls needs something from there to level up) and saw this: https://gyazo.com/c5bfdcff0aad008c096705fec078169b . Its hard to buy anything if the merchant sells nothing. The same happened in Umbra.

Btw, i had no quest to go to Gorn, i went there only for the item that i need.

No bug here, you simply don't have any types of items selected in the filters at the top left.  On Discord I have a bugfix patch that includes a quality of life improvement of defaulting the filters to showing everything each time an inventory screen opens.

edit: grammar

So the game removes the filters after a while by itself? Sounds like a bug to me, because normally the filter for "All Goods" is automatically selected.