It is possible to crash the generator, so that it will only show the blank background of the last used colour. You can only see the fullscreen button, which is working, but clicking anywhere else or trying to use keyboard to generate a city proves innefective.

It most likely occurs, when you click on a link on the page (i.e. the itch.io links on the right side of the page) and redirect yourself from it, you try to go back and you realise that the generator doesn't work. 

The bug seems to be independent of the browser you use, it happened to me with Mozilla Firefox and Microsoft Edge. Refreshing the page,  restarting the browser and deleting the itch.io cookies don't help. If anything changes, i will update.

I hope the bug will be found and eliminated soon, if anybody knows a solution, please share. Thank you!

EDIT: Restarting the computer didn't help either. Other creations are not influenced and i could not crash them this way.

I found a half-solution for firefox: Right click on the blank window, then choose This Frame, now you see a number of options. With the first 3, you will be able to use the city generator as a whole page, which may not be necessarily the best, since you cannot zoom and use full-screen mode, but better than nothing. Reload Frame doesn't do much and the other options aren't really useful either, at least for me. However, if you change the colour palette in the generator in the new window and reload the site, the colour of the blank canvas will change accordingly. I hope this'll help a little bit locate the source of the problem. Sadly, i couldn't find an similar option in the microsoft edge.

Here is my very short list of ideas:

1. Try the non-itch version: http://fantasycities.watabou.ru/. It is identical, but probably works better without itch.io interfering.
2. Try clearing the cache. All that is saved locally is settings, but maybe your browser restores the generator is some "bad" state, which prevents him from working normally.