Strange issue on flight plan SESM-SELT

[CS-TMT 11]

Hello sirs.

 

After trying a flight plan from SPZO (Cuzco, Peru) to SESM (Shell Mera-Rio Amazonas, Ecuador) with SELT (Cotopaxi) as alternate I came to a strange issue: no matter what airplane I choose, when pushing "compute flight" button PFPX always returns a message saying that the required fuel exceeds the aircraft's maximum fuel capacity (it is a ~900nm flight!), even with an Airbus or Boeing, just, as I said, regardless of what airplane I choose.

Then, after choosing "no alternates" to see wheter the issue was the flight plan itself or the route to alternate, I found that the issue was with the alternate route. SESM and SELT are only 48nm apart from each other, so it's strange for me that the needed fuel exceeds maximum fuel capacity.
Now, when trying to build a flight plan only between SESM and SELT, it gives me some weird values as well (but at least lets me compute the flight, though it takes around 2min to compute).

Here is a screenshot. What's wrong with this flight plan?
 

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[X24 1]

I am getting the same result

[CS-TMT 11]

Found out the issue was SESM. One thing I didn't notice is that this runway is quite short andat a certain altitude. Could it be that PFPX can't calculate propper values due to the shortness of the runway being it too short for an A319?