All of a sudden, my Dvar prospectors can't prospect ...

[The Grumpy Buddha]

Does anyone have any idea why, after prospecting a massive ton for the rest of the game, suddenly I can't prospect anywhere, regardless of the type of territory?

 

[Ridixo]

Report the bug
The symbol is there, you should be able to do it

 

[The Founder]

IIRC, each sector can only be prospected once - all dvar have to share that number.

It is rather odd the sector is show as being Prospectable. Maybe it was terraformed? There are often issues with uninhabitable sectors being terraformed but not properly set up for every rule.