Turn order not functioning at all

I played yesterday with my group and the turn order simply did not work:
I opened the turn order widget as usual.
Then I wanted to add a player's token to the turn order by right-clicking and choosing "Add Turn" in the pop up menu
The turn order widget remained empty (except for its title and the buttons below)

I also tried to add a Custom Item:
I clicked on the blue gear-wheel
The "Turn Order Settings" widget showed.
I added some "Item Label" and clicked on "Add" right next to it.
The turn order widget was unaffected.

Is this a known issue? If it's of any relevance: the campaign is here: https://app.roll20.net/campaigns/details/470039/stadtpflanzen-und-landeier

Seems that I could solve the problem.
My turn order widget was completely empty where normally the text "There aren't currently any tokens..." is shown.
So I just clicked on the blue gear-wheel, and then clicked on the red button "Remove All Turns (clear list)".
Now I have my normal turn order widget again.

If I am able to reproduce the problem again, I'll try to give detailed how-to-steps.
In the meantime, this post should be closed.

FYI, we just ran into this same bug in our campaign. The above fix resolved the issue.

Please let us know if you can figure out how to reproduce the behavior.

This just happened in our campaign as well, and clearing the list solved the problem.

Can you provide the steps you performed that caused the problem? This is so the devs can reproduce it and figure out why it is happening then solve it.