I have had this happen sometimes. But I am surprised that it happened at 300 ft since the larger FOV should allow each image to have more areas to match points in. Flying with all oblique images could help since they will have a larger FOV
Were...
The best zoom for less than $10K is the Matrice 4 E or an Autel Evo Max. The Matrice 4 E is only a notch below the Matrice 30 series. It is truly a creeper zoom.
Is the area too homogeneous such as being just trees? The other areas have bald spots and roads which would work better with photogrammetry. I have had heavily forested areas not process on different occasions.
What was the flight height (GSD)...