Basically what happens is I setup a trade route with multiple cities and when clicking Quit the route clears itself.
The cities are still there, but all the goods actions (buy, sell, etc) are gone. If I save the route and load it afterwards, is empty aswell.
If I enable the route the ship departs to the next city, but then it gets interrupted as all the actions are gone again.

Anybody knows whats going on here?

This took me some time to figure out. You must set quantity, if it is zero it clears itself. I usually set all to max.

Make also sure to tweak the prices a little bit, the default prices are too low to buy anything.

Hi
There has to be either Max for amount OR u Have to specify How much to buy or sell
At what price for both Buy and Sell

Be aware as the game progresses that certain goods will become cheaper both to buy and sell, so u might end up with 1 type of goods on an entire convoy without it moving in one cycle... If its high end stuff, it might take u a while to move all those goodies

Also Note where u have ur fleet set for auto repair, Friendly ports will cost way less to repair.