What a mess, more than 50 issues pending
When seeing the mess in that code, I conclude that this Gnome must have gone totally blind on both eyes. I therefore suggest renaming the project to "Blind eyes of gnome" or short "BOG", which also is an appropriate denotation for this project.
Reasoning:
a) When opening a single picture in a directory holding 1'000 images (which today is a moderate number), it may take up to 30 seconds until the first image is displayed. Please admire EOM (Eye Of Mate) and many others, who show that image within a fraction of a second.
b) In case you should be too demanding and activate the display of thumbnails, there is a fair chance that BOG crashes after having eaten all your free Gigabytes of RAM.
c) Display of key bindings in the main menu shows only 3 of about a dozen used in BOG.
d) I have quite some doubts that the plugin mechanism is functional as advertised.
This whole mess is known and documented for many years and I suggest that the famous maintainers of Gnome in the near future repair the code or withdraw it, because it is an imposition and not a solution.