Hi Goran -- Have you shared your map with any groups? Workforce shows you the maps that can be used in Collector that you have shared with groups, which is also how others will be able to access the map in Collector.
Sharing with the whole org won't work -- it is group-based sharing. I found that I had to refresh the Workforce app if I was already in the middle of project creation when I shared my map with an individual group. Were you changing the map's sharing while you were also working in Workforce?