Valve retainers
Can't tell for sure with those pics as there are a lot of shadows. The first pic is the only pic that looks like the right valve MIGHT have a cracked retainer. The others just look like poor lighting/shadowing giving the appearance of sunken keepers. If you can, retake the pics and have better backlighting/different angle/flash and I should be able to give you a more definitive answer.
Look at the keepers, good retainers in addition to not having sunken keepers also space the keepers evenly appart. Notice how your keepers are touching?
If you want to know for sure use a dentist mirror with a light and look under the retainers.
If you want to know for sure use a dentist mirror with a light and look under the retainers.











