What is the meaning of uppajjati versus upapajjati?
I think there are two rather different words confused here.

One is Sanskrit "utpada"/"anutpada" (to arise / not to arise) and its Pali corruption "uppada" with a past form "uppanna".

Another one is Sanskrit "upaprajati" (something like "offshoot" or "derivative" - meaning something that is born off a family but separate) and the Pali corruption of its past form, "upapanna".

Google dictinary for "offshoot" gives the following meanings:


  
  a thing that originated or developed from something else.
  "commercial offshoots of universities"
    synonyms: outcome, result, (side) effect, corollary, consequence, upshot, product, by-product, spin-off, development, outgrowth, fallout
    "rap music began as an underground offshoot of disco"
  subsidiary, branch, adjunct, derivative
    "the company now controls several offshoots"
  


Checking the examples of sutta usages in @ChrisW's answer, I think they all make sense.