Plex Photos error

[beckfield]

How large are the files that fail to load?

Plex has an undocumented limit of 100 MiB for photos. This can be overridden, with caution. See this earlier post:

Android app won't display large pictures

By default, Plex won’t display photos over 100 Mib (Mebibytes - I had to look that up when I learned about this limit). This is a server-side limit, rather than the app. There is an override, to be used with caution, since the limit is there for performance reasons. See this page, and look for the TranscoderPhotoFileSizeLimitMiB advanced setting: https://support.plex.tv/articles/201105343-advanced-hidden-server-settings/