Only some images show in emails

v3.6.13

Don’t know what’s going on here but some images load and others don’t.
I’ve triple-checked settings and all is normal. Emails get sent, but people are reporting only some images load. I’ve checked the size and dimensions of all images and they are all normal.
My image directory is under webroot directory under ‘images’:
UPLOADIMAGES_DIR’, ‘/images’);
When I load images the gui comes up and I am able to choose the images I want.
Any help much appreciated and I’m under some pressure as a mailing was supposed to go out yesterday and with people saying they are only getting some images I’m a bit frazzled. . .

Solved:
After much investigation it seems like emails sent from phplist and opened on an android phone (this probably apply for other newsletter systems) AND if the recipient archives the message ON THEIR PHONE in gmail rather than deleting it subsequent emails with the same content (i.e. sending test message) or similar (with the same images, it seems) will not all load. If you then delete the message AND clear the cache on your phone, they all will appear in follow up email messages.

At least that is what was happening to me on an android phone. This wasn’t happening on the desktop computer but I would need to choose from the email client to “display images”.

Very strange.