Each AI voice database is based on machine learning analysis of a real human singer, so they inherit articulation and pitch behaviors similar to the original voice provider.
In this case the slight timing differences are likely a result of Kevin and Solaria’s voice providers articulating the lyrics differently when they sing, and the synthesis engine attempting to replicate that.
Pitch differences are a result of Sing mode re-generating the curves based on the original voice provider’s singing style, such as their tendency to under/overshoot notes, where they use vibrato, etc.
Timing adjustments have to be done on a case-by-case basis, but you can avoid the software re-generating the pitch curve by switching the notes to Manual mode before copying. Make sure to also right click on the selection and use “Select Parameters for Notes” (ctrl+alt+A) to keep all the parameter data when copying.