Hi Kirk,
No eureka moment but some info that may be helpful.
1. I selected 5 raw files and applied processing in a set of additional steps:
(a) opened the raw file in the develop module, no processing, no duplicate layer - saved as .aphoto file - all five displayed previews correctly when ingested to PM
(b) opened the raw file, no processing, duplicated and locked the raw layer in the photo persona - saved as .aphoto file - all five displayed previews when ingested
(c) opened one of the raw files, duplicated and locked the raw layer, added one live filter layer - saved as .aphoto file - preview displayed correctly
(d) opened the same raw file, duplicated and locked the raw layer, added one live adjustment layer - saved as .aphoto file - preview displayed correctly
(e) opened the same raw file, duplicated and locked the raw layer, added 3 live filter layers and 2 live adjustment layers - saved as .aphoto file - preview would not display
Aha! - but aha turned into WTF because:
(f) opened the same raw file, duplicated and locked the raw layer, added the same 3 live filter layers and same 2 live adjustment layers - saved as .aphoto file - preview displayed correctly
(g) opened the same raw file and repeated (e) and (f) but kept adding more filter and adjustment layers and all of the saved .aphoto files correctly displayed the .aphoto files.
I have attached the log file. I changed the file names as I went so I may have added some confusion there. I am using the latest release of Affinity Photo - 2.6.2
I will play a bit more to try and understand why .aphoto files are generated that that do not display previews correctly. My previous screenshots included files processed with version 2.6.0, 2.6.1 and 2,6 beta versions.
Hope this helps.
Steve