Tie won't flip

I have a note that is four semibreves over four bars of 4/4.
The tie from semibreve 2 to 3 is downwards. If I flip the tie, the others move but not that one.
If I cut it and retie, I get the same.
It is not a slur, nor are any notes in different voices.

Any ideas?

You can’t select just that tie in Engrave mode and override its direction via Properties? Please attach the project if you find this doesn’t work.

That wasn’t working. I deleted the whole passage and input again as two breves and it was fine. Thanks for help.