Can a lip augmentation with Juvederm Ultra plus shrink/dissolve? Even though they are yearly? For instance laying out in the sun

Juvederm is attracted to water, so when you're tanning, you may be dehydrated which appears to shrink the filler. Moisturizing and making sure you drink lots of fluids should give improvement. Hope this helps.

Juvederm is hydrophilic which means it is attracted to water.  When you are dehydrated, your lips will be dehydrated as well.  Therefore, laying out in the sun may indeed make your lips appear smaller in the short term.  Rubbing your lips together frequently may also shorten the life of the Juvederm in your lips.  

This may be due to dehydration which is causing it to appear like your juvederm results are dissolving. I recommend following up with your injector about your concerns. A different filler may yield better results. Implants or fat are an alternative. Best, Dr. Emer