thanks for reporting the issue! I just tried to reproduce this in a similar setting (existing large photo library accessed over a network share) and was able to produce two issues. One is likely specific to my particular import folder’s access rights and was not causing an application crash, but the second one was a crash happening after checking the “Import photos from sub folders” check box, and looks like a good candidate for the issue you described.
The crash is fixed in our development branch and, if possible, it would be great if you could try to reproduce your original crash with the next preview release (1.0.0-preview.8), which should be out some time later this month. This may require deleting the global metadata cache in
Should it still reproduce then, there should be a stack trace at the end of
%TEMP%/aspect-log.html that may contain enough information for us to find and fix the issue.
The bug is tracked internally as #515.