That is probably the cause. PSD can only save up to 2GB. Anything over 2GB has to be saved as PSB (Photoshop large format). I think layered TIF can save up to 4GB so that is probably why he saved the document as a TIF instead of PSD. SPA doesn’t have options to save as layered PSD or layered TIF.
I never created those options because I didn’t think many people would want to run batches saving over 2GB per images. Say your image was 4GB and you batch 100 fileas, that would be 400GB of disk space just for those 100 images. Also, when saving files that larger it would run pretty slow having to save that large of files. An SSD would maybe not be so bad. However, if not an SSD it would be painfully slow to batch.
late and consolidating as many layers as you can. Try to get the template down to 1 GB or so when saved as PSD. When adding the Pixnub layers, it will increase the file size. So just make sure with the Pixnub layers added it is under 2GB and it will batch. Since there will be variations in size image to image, don’t cut it too close to the 2GB. I would try to give some extra room. So maybe 1.5GB with all Pixnub layers added.
Also, make sure the template is set to sRGB too. This opens up possibilities for color shifting when making composites. Plus when making paper prints, most photo labs want sRGB… and they will convert it to sRGB if you send them something else anyway.
Without getting into tech details, it is a mistake to use Adobe RGB 1998 unless you are printing metal prints or something like that that could benefit from Adobe RGB 1998. Anyway just check the template. I think some of his older templates were Adobe RGB 1998 but he then started making sRGB later. So it could be either for your template.