I also had problems getting WebODM or Open Drone Map to process forest images. Using defaul settings, I would either get an error or a partial reconstruction using less than a quarter of the images. Following suggestions in the forum, I increased the min-num-features to the 12000 to 24000 range and use pmvs. I still have some images omitted from the analysis, but rerunning can improve the resulting orthomosaic. I suspect that the random process of obtaining strips from each image influences successful matching. I also found that I had to fly missions at higher altitudes (100 to 120 m). I haven’t been able to process images from missions at the 40 to 50 m altitude with 80% overlap. I suspect that I would have to increase overlap to 90%.
The other issue with processing images with ODM is failure to allocate sufficient memory for the application. I had to set up a virtual server running Ubuntu to finally succeed in processing images. I adhere to the minimum recommended configuration, but still have occasional failures due to memory issues. Parallax issues and uniformity of forest cover create problems for ODM and other mapping software. Nevertheless, you can get partial reconstructions from ODM by increasing min-num-features and using the pmvs option. If you encounter memory issues, you will need to migrate your application to a larger platform.