RH HTML 2015. Image preview not working for some PNGs during Insert image.
I have five PNG files in a topic do not "preview" when selected in Insert > Image. The Preview pane displays a red box.

When I preview the topic, the images appear correctly.
I thought that the file names might be too long, but I verified that other PNGs with lengthy file names appear correctly.
I thought that the PNGs might be too larger, but other PNGs of greater size preview correctly.
Are there any restrictions related to images in terms of file name length or size?
Thanks for any help on this issue.
Regards,
Carol Levine
